HK1160682A - Method and device for packaging a substrate - Google Patents

Abstract

A package structure and method of packaging for an interferometric modulator. A thin film material is deposited over an interferometric modulator and transparent substrate to encapsulate the interferometric modulator. A gap or cavity between the interferometric modulator and the thin film provides a space in which mechanical parts of the interferometric modulator may move. The gap is created by removal of a sacrificial layer that is deposited over the interferometric modulator.

Description

Method and apparatus for packaging a substrate

Related information of divisional application

This application is application No. 200510102599.0; the application date is 9/12/2005; divisional application of the invention patent application entitled "method and apparatus for packaging a substrate".

Technical Field

The technical field of the invention relates to micro-electromechanical systems (MEMS) and packaging of such systems. More specifically, the technical field of the invention relates to interferometric modulators and methods of making such modulators using thin film backplanes.

Background

Microelectromechanical Systems (MEMS) include micromechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is known as an interferometric modulator. An interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. One of the plates may comprise a stationary layer deposited on a substrate and the other plate may comprise a metal diaphragm separated from the stationary layer by an air gap. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their performance can be exploited in improving existing products and creating new products that have not yet been developed.

Disclosure of Invention

The system, method and apparatus of the present invention have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of the invention, its more prominent features will now be discussed briefly. After reviewing this discussion, and particularly after reading the section entitled "detailed description of certain embodiments" one will understand how the features of this invention provide advantages over other display devices.

An embodiment provides a package structure for an interferometric modulator display device that eliminates the need for separate backplates, desiccants, and seals. The display device includes a transparent substrate, an interferometric modulator configured to modulate light transmitted through the transparent substrate, and a thin film backplane disposed over the modulator and sealing the modulator within a package between the transparent substrate and the thin film backplane. There is a gap between the modulator and the membrane, which is formed by removing a sacrificial layer.

According to another embodiment, a method of manufacturing a display device is provided. According to the method, a transparent substrate is provided and an interferometric modulator is formed on the transparent substrate. A thin film backplane is then deposited over the interferometric modulator and the transparent substrate to seal the modulator between the transparent substrate and the thin film backplane. A sacrificial layer is deposited over the interferometric modulator prior to depositing the thin film backplane. After depositing the thin film backplane, the sacrificial layer is removed to form a gap between the interferometric modulator and the thin film backplane.

In accordance with yet another embodiment, a MEMS display device is provided that includes a transparent substrate, an interferometric modulator formed on the transparent substrate, and a thin film backplate sealed to the transparent substrate to encapsulate the interferometric modulator between the transparent substrate and the thin film backplate. A cavity exists between the interferometric modulator and the thin film backplane. The cavity is formed by removing a sacrificial layer between the interferometric modulator and the thin film backplate.

In accordance with another embodiment, a display device is provided that includes a transparent substrate, an interferometric modulator, a thin film backplane deposited over the interferometric modulator, and a cavity between the modulator and the thin film backplane. The interferometric modulator is configured to modulate light transmitted through the transparent substrate and is formed on the transparent substrate. The thin film backplane is deposited on the interferometric modulator to seal the modulator within a package between the transparent substrate and the thin film backplane. The cavity is formed by removing a sacrificial material.

According to yet another embodiment, a display device is provided. The display device includes a transmitting member for transmitting light, a modulating member configured to modulate the light transmitted through the transmitting member, and a sealing member for sealing the modulating member in a package between the transmitting member and the sealing member. The modulating member comprises an interferometric modulator, and the sealing member comprises a membrane.

Drawings

These and other aspects of the invention will be apparent from the following description and from the accompanying drawings (not to scale), which are intended to illustrate and not to limit the invention, and in which:

FIG. 1 is an isometric view depicting a portion of one embodiment of an interferometric modulator display in which a movable reflective layer of a first interferometric modulator is in a released position and a movable reflective layer of a second interferometric modulator is in an actuated position.

FIG. 2 is a system block diagram illustrating one embodiment of an electronic device including a 3x3 interferometric modulator display.

FIG. 3 is a diagram of the position of the movable mirror versus applied voltage for one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is a schematic diagram of a set of row and column voltages that may be used to drive an interferometric modulator display.

FIGS. 5A and 5B show an exemplary timing diagram for row and column signals that may be used to write a frame of display data to the 3x3 interferometric modulator display of FIG. 2.

Fig. 6A is a cross-sectional view of the device of fig. 1.

FIG. 6B is a cross-sectional view of an alternative embodiment of an interferometric modulator.

FIG. 6C is a cross-sectional view of another alternative embodiment of an interferometric modulator.

FIG. 7 schematically shows a package structure in which an interferometric modulator is packaged without using a conventional backplate, according to an embodiment.

FIG. 8 is a flow diagram of an embodiment of a method for packaging interferometric modulators.

FIG. 9 schematically shows a package structure in which a sacrificial layer has been deposited over an interferometric modulator, according to an embodiment.

FIG. 10 schematically shows a package structure in which a thin film has been deposited on a sacrificial layer.

FIG. 11 is a top view of an embodiment of a package structure 800 after the thin film 820 has been deposited and patterned, before the sacrificial layer 850 is released.

FIG. 12 schematically illustrates a package structure in which an interferometric modulator is packaged according to one embodiment and has an overcoat layer.

FIGS. 13A and 13B are system block diagrams illustrating one embodiment of a visual display device comprising a plurality of interferometric modulators.

Detailed Description

The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In the description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the invention may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More specifically, the invention encompasses: embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, the following: mobile telephones, wireless devices, Personal Data Assistants (PDAs), handheld or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., rangefinder display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar construction to the MESE devices described herein can also be used in non-display applications such as in electronic switching devices.

An interferometric modulator display embodiment comprising an interferometric MEMS display element is shown in FIG. 1. In these devices, the pixels are in either a bright or dark state. In the bright ("on" or "open") state, the display element reflects a large portion of incident visible light to the user. When in the dark ("off" or "closed") state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the "on" and "off" states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series of pixels of a visual display, wherein each pixel comprises a MEMS interferometric modulator. In certain embodiments, an interferometric modulator display comprises a row/column array of these interferometric modulators. Each interferometric modulator includes a pair of reflective layers positioned at a variable and controllable distance from each other to form a resonant optical cavity with at least one variable dimension. In one embodiment, one of the reflective layers is movable between two positions. In the first position, referred to herein as the released state, the movable layer is positioned relatively far from a fixed partially reflective layer. In the second position, the movable layer is positioned closer to the partially reflective layer. Incident light that reflects from the two layers interferes constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel.

The portion of the pixel array shown in FIG. 1 includes two adjacent interferometric modulators 12a and 12 b. In the interferometric modulator 12a on the left, a movable highly reflective layer 14a is illustrated in a released position at a predetermined distance from a fixed partially reflective layer 16 a. In the interferometric modulator 12b on the right, a movable highly reflective layer 14b is illustrated in an actuated position adjacent to a fixed partially reflective layer 16 b.

The fixed layers 16a, 16b are electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more layers each of chromium and indium tin oxide on a transparent substrate 20. The layers are patterned into parallel strips and may form row electrodes in a display device, as will be described further below. The movable layers 14a, 14b may be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes 16a, 16 b) deposited on top of posts 18 and an intervening sacrificial material deposited between the posts 18. After the sacrificial material has been etched away, the deformable metal layers are separated from the fixed metal layers by a defined air gap 19. The deformable layers may be formed from a highly conductive and reflective material, such as aluminum, and the strips may form column electrodes in a display device.

When no voltage is applied, the cavity 19 remains between the layers 14a, 16a, and the deformable layer is in a mechanically relaxed state as illustrated by the pixel 12a in FIG. 1. However, after application of a potential difference to a selected row and column, the capacitor formed at the intersection of the row and column electrodes at the corresponding pixel becomes charged, and electrostatic forces pull the electrodes together. If the voltage is high enough, the movable layer deforms and is forced against the fixed layer (a dielectric material (not shown in this figure) may be deposited over the fixed layer to prevent shorting and control the separation distance), as shown in the right pixel 12b in FIG. 1. The behavior is the same regardless of the polarity of the applied potential difference. It can thus be seen that row/column actuation that can control the reflective vs. non-reflective pixel states is analogous in many ways to that used in conventional LCD and other display technologies.

FIGS. 2-5 illustrate one exemplary process and system for using an array of interferometric modulators in a display application. FIG. 2 is a system block diagram illustrating one embodiment of an electronic device that may embody aspects of the invention. In the exemplary embodiment, the electronic device includes a processor 21, which may be any general purpose single-or multi-chip microprocessor, such as an ARM,PentiumPentiumPentiumPro、8051、PowerOr any special purpose microprocessor such as a digital signal processor, microcontroller, or programmable gate array. As is conventional in the art, the processor 21 may be configured to execute one or more software modules. The processor may be configured to execute in addition to executing an operating systemOne or more software applications, including a web browser, a telephone application, an email program, or any other software application.

In one embodiment, the processor 21 is further configured to communicate with an array controller 22. In one embodiment, the array controller 22 includes a row driver circuit 24 and a column driver circuit 26 that provide signals to a pixel array 30. The cross-sectional view of the array shown in FIG. 1 is shown by line 1-1 in FIG. 2. For MEMS interferometric modulators, the row/column actuation protocol may take advantage of the hysteresis properties of these devices shown in FIG. 3. It may require, for example, a 10 volt potential difference to cause a movable layer to deform from the released state to the actuated state. However, when the voltage is reduced from this value, the movable layer will retain its state as the voltage drops back below 10 volts. In the exemplary embodiment of FIG. 3, the movable layer does not release completely until the voltage drops below 2 volts. Thus, in the example shown in FIG. 3, there is a range of voltage, approximately 3-7 volts, within which there exists a window of applied voltage within which the device is stable in either the released or actuated state. This is referred to herein as the "hysteresis window" or "stability window". For a display array having the hysteresis characteristics of FIG. 3, the row/column actuation protocol can be designed to apply a voltage difference of about 10 volts to the pixels to be actuated in the selected pass and a voltage difference of approximately 0 volts to the pixels to be released during row strobing. After the strobe, the pixels are exposed to a steady state voltage difference of about 5 volts such that they remain in whatever state the row strobe put them in. After being written, each pixel sees a potential difference within the "stability window" of 3-7 volts in this example. This feature makes the pixel design shown in fig. 1 stable under the same applied voltage conditions in either an actuated or released pre-existing state. Since each pixel of the interferometric modulator, whether in the actuated or released state, is essentially a capacitor formed by the fixed and moving reflective layers, this stable state can be held at a voltage within the hysteresis window with almost no power dissipation. Essentially no current flows into the pixel if the applied potential is constant.

In typical applications, a display frame may be created by asserting the set of column electrodes in accordance with the desired set of actuated pixels in the first row. A row pulse is then applied to the row 1 electrode, actuating the pixels corresponding to the asserted column lines. The asserted set of column electrodes is then changed to correspond to the desired set of actuated pixels in the second row. A pulse is then applied to the row 2 electrode, actuating the appropriate pixels in row 2 in accordance with the asserted column electrodes. The row 1 pixels are unaffected by the row 2 pulse, and thus remain in the state they were set to during the row 1 pulse. The above steps may be repeated for the entire series of rows in a sequential manner to form the frame. Typically, the frames are refreshed and/or updated by repeating the process at some desired number of frames per second. A wide variety of protocols for driving row and column electrodes of pixel arrays to produce display frames are also well known and may be used in conjunction with the present invention.

Fig. 4 and 5 show one possible actuation protocol for forming a display frame on the 3x3 array of fig. 2. FIG. 4 shows a possible set of row and column voltage levels that may be used for pixels having the hysteresis curves of FIG. 3. In the embodiment of FIG. 4, actuating a pixel involves setting the appropriate column to-Vbias, and the appropriate row to + Δ V, which may correspond to-5 volts and +5 volts, respectively. Releasing a pixel is accomplished by setting the corresponding column to + Vbias, and the corresponding row to the same + deltav, thereby creating a 0 volt potential difference across the pixel. In those rows where the row voltage is held at 0 volts, the pixels are stable in the state they were originally in, being at + V with the column_biasOr is-V_biasIs irrelevant.

FIG. 5B is a timing diagram showing a series of row and column signals applied to the 3 × 3 array of FIG. 2, which will result in the display arrangement of FIG. 5A, where actuated pixels are non-reflective. Prior to writing the frame shown in FIG. 5A, the pixels can be in any state, in this example, all the rows are at 0 volts, and all the columns are at +5 volts. Under these applied voltages, all pixels are stable in their existing actuated or released states.

In the frame shown in FIG. 5A, pixels (1, 1), (1, 2), (2, 2), (3, 2) and (3, 3) are activated. To accomplish this, column 1 and column 2 are set to-5 volts, and column 3 is set to +5 volts for a row time in row 1. This does not change the state of any pixels, since all pixels remain within the 3-7 volt stability window. Thereafter, row 1 is strobed with a pulse that rises from 0 volts to 5 volts and then falls back to 0 volts. Thereby actuating the pixels (1, 1) and (1, 2) and releasing the pixels (1, 3). No other pixels in the array are affected. To set row 2 as desired, column 2 is set to-5 volts, and columns 1 and 3 are set to +5 volts. Thereafter, applying the same strobe to row 2 will actuate pixel (2, 2) and release pixels (2, 1) and (2, 3). Again, no other pixels in the array are affected. Similarly, row 3 is set by setting columns 2 and 3 to-5 volts, and column 1 to +5 volts. The row 3 strobe sets the row 3 pixels to the state shown in FIG. 5A. After writing the frame, the row potentials are 0, while the column potentials can remain at either +5 or-5 volts, and the display will thereafter be stable in the arrangement shown in FIG. 5A. It will be appreciated that the same procedure can be used for arrays consisting of tens or hundreds of rows and columns. It will also be appreciated that the timing, sequence, and levels of voltages used to perform row and column actuation can be varied widely within the general principles outlined above, and the above example is exemplary only, and any actuation voltage method can be used with the present invention.

The detailed structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example, FIGS. 6A-6C show three different embodiments of the moving mirror structure. FIG. 6A is a cross-sectional view of the embodiment of FIG. 1, wherein a strip of metal material 14 is deposited on orthogonally extending supports 18. In FIG. 6B, the moveable reflective material 14 is attached to supports at the corners only, on tethers 32. In FIG. 6C, the moveable reflective material 14 is suspended from a deformable layer 34. This embodiment has advantages because the structural design and materials used for the reflective material 14 can be optimized with respect to the optical properties, and the structural design and materials used for the deformable layer 34 can be optimized with respect to desired mechanical properties. The production of various types of interference devices is described in a number of published documents, including, for example, U.S. published application No. 2004/0051929. The above-described structures may be fabricated using a variety of well-known techniques, including a series of material deposition, patterning, and etching steps.

FIG. 7 shows a package structure 800 in which an interferometric modulator 830 is packaged on a transparent substrate 810 without the use of a conventional backplate or cap. The package structure 800 shown in FIG. 7 may eliminate the need to use not only a backplane but also a separate seal and desiccant.

According to the embodiment of FIG. 7, rather than sealing a backplate to a transparent substrate to encapsulate the interferometric modulator 830 as described above, a thin film or superstructure 820 is deposited on the transparent substrate 810 to encapsulate the interferometric modulator 830 within the package structure 800. The thin film 820 may protect the interferometric modulator 830 from harmful elements in the environment.

One method of packaging interferometric modulators in accordance with the embodiment shown in FIG. 7 will be discussed in greater detail below. The packages and packaging methods described herein may be used to package any interferometric modulator, including but not limited to the interferometric modulators described above.

As described above, the interferometric modulator 830 is configured to reflect light through the transparent substrate and includes moving parts, such as the movable mirrors 14a, 14 b. Thus, to enable the moving parts to move, a gap or cavity 840 is preferably formed between the moving parts and the thin film 820. The gap or cavity 840 enables the mechanical components of the interferometric modulator 830, such as the movable mirrors 14a, 14b, to move. It should be appreciated that before the thin film 820 may be deposited to encapsulate the interferometric modulator 830, a sacrificial layer 850 (shown in FIG. 9) is preferably deposited over the interferometric modulator 830 and the transparent substrate 810 and then removed to form a cavity 840 between the interferometric modulator 830 and the thin film 820. This will be explained in further detail below.

FIG. 8 shows one embodiment of a method of packaging an interferometric modulator without the use of a conventional backplate or cap. A transparent substrate 810 is first provided in step 900, and the interferometric modulator 830 is formed on the transparent substrate 810 in step 910. The interferometric modulator 830 is preferably formed in accordance with the process described with reference to FIGS. 1-6. The transparent substrate 810 may be any transparent substance capable of having a thin film, MEMS device formed thereon. Such transparent substances include, but are not limited to, glass, plastic, and transparent polymers. The image is displayed through a transparent substrate 810 that serves as an imaging surface.

After the interferometric modulator 830 has been formed on the transparent substrate 810, a sacrificial layer 850 is preferably deposited on the interferometric modulator 830 and the upper surface of the transparent substrate 810 in step 920. The sacrificial layer 850 is then patterned in step 930 using photolithographic techniques. The patterning process preferably localizes the sacrificial layer 850 to the interferometric modulator 830, exposing the transparent substrate 810 around the perimeter of the interferometric modulator 830. After the sacrificial layer 850 has been deposited and the sacrificial layer 850 patterned, a thin film 820 is then deposited over the entire structure in step 940. The thin film 820 is then patterned using photolithography techniques in step 950. This patterning process confines the thin film 820 to only the sacrificial layer 850. This patterning step also provides topography in the thin film 820 that enables subsequent removal of the sacrificial layer 850. It should be noted that at this point in the process, additional sacrificial layers may or may not remain within the interferometric modulator structure. The patterning step 930 enables the sacrificial layer 850 to be removed as well as removing any sacrificial layer remaining within the interferometric modulator 830. In step 960, the sacrificial layer 850 and any sacrificial layers within the interferometric modulator 830 are removed, leaving a cavity 840 between the interferometric modulator 830 and the thin film 820, thereby completing the processing of the interferometric modulator 830. In step 970, the features or openings in the thin film 820 are sealed.

According to one embodiment, an interferometric modulator 830 is preferably formed on a transparent substrate 810. It should be appreciated that the fixed mirrors 16a, 16b of the interferometric modulator 830 are adjacent the transparent substrate 810, and the movable mirrors 14a, 14b are formed on the fixed mirrors 16a, 16b in a manner that allows the movable mirrors 14a, 14b to move within the cavity 840 of the package structure of the embodiment shown in FIG. 7.

To form the interferometric modulator 830, the transparent substrate 810 is covered with Indium Tin Oxide (ITO) in one embodiment. The ITO may be deposited by standard deposition techniques including Chemical Vapor Deposition (CVD) and sputtering, preferably to a thickness of about 500 angstroms. A relatively thin layer of chromium is preferably deposited on the ITO. The ITO/chrome bilayer is then etched and patterned into columns to form the column electrodes 16a, 16 b. Preferably, a layer of silicon dioxide (SiO) is formed on each ITO/chrome column₂) To form partially reflective fixed mirrors 16a, 16 b. A sacrificial layer of silicon (Si) is preferably deposited (and subsequently released) over the structure to form an optical resonator between the fixed mirrors 16a, 16b and the movable mirrors 14a, 14 b. In other embodiments, the sacrificial layer may be formed of molybdenum (Mo), tungsten (W), or titanium (Ti).

Another mirror layer, preferably formed of aluminum, is deposited over the sacrificial layer of silicon to form the movable mirrors 14a, 14b of the interferometric modulator 830. The mirror layer is deposited and patterned into rows orthogonal to the column electrodes 16a, 16b to form the row/column array described above. In other embodiments, the mirror layer may comprise a highly reflective metal such as, for example, silver (Ag) or gold (Au). Alternatively, the mirror layer may be a metal stack configured to provide appropriate optical and mechanical properties.

After the movable mirrors 14a, 14b are formed, the sacrificial layer of silicon is removed, preferably using a gas etch process, to form an optical cavity between the fixed mirrors 16a, 16b and the movable mirrors 14a, 14 b. In one embodiment, the sacrificial layer is etched away after the thin film 820 is formed. The sacrificial layer of silicon may be removed using standard etching techniques. The particular release etch will depend on the material to be released. For example, xenon difluoride (XeF) can be used₂) The sacrificial layer of silicon is removed. In one embodiment of the present invention, the substrate is,after the thin film 820 is formed, the sacrificial layer of silicon between the mirrors 16a, 16b, 14a, 14b is removed. Those skilled in the art will appreciate that each layer of the interferometric modulator 830 is preferably deposited and patterned using standard deposition techniques and standard photolithographic techniques.

As shown in FIG. 9, after the interferometric modulator 830 is formed on the transparent substrate 810, another sacrificial layer 850 is deposited on the interferometric modulator 830 and the upper surface of the transparent substrate 810. The sacrificial layer 850 may be made of a material that can be released after deposition of the thin film 820, such as, for example, molybdenum (Mo), silicon (Si), tungsten (W), or titanium (Ti). In one embodiment, the sacrificial layer 850 is made of a material such as a polymer, spin-on glass, or oxide. The removal processes, which may vary depending on the material of the sacrificial layer, will be described in more detail below.

Those skilled in the art will appreciate that the upper sacrificial layer 850 may be formed of any of molybdenum (Mo), silicon (Si), tungsten (W), titanium (Ti), polymer, spin-on glass, or oxide, as long as the material provides sufficient step coverage and can be deposited to a desired thickness. The thickness of the sacrificial layer 850 should be sufficient to separate the thin film 820 from the interferometric modulator 830. In one embodiment, the upper sacrificial layer 850 is deposited to a thickness in the range of about 1000A to 1 micron, more preferably in the range of about 1000A to 5000A. In one embodiment, the sacrificial layer 850 is patterned and etched using standard photolithographic techniques.

In one embodiment, the thin film 820 may be deposited on the entire upper surface of the sacrificial layer 850 as shown in FIG. 10. The thin film 820 may be formed on the sacrificial layer 850 using known deposition techniques. After the thin film 820 is patterned and etched, the sacrificial layer 850 is released to form a cavity 840 in which the movable mirrors 14a, 14b can move, as shown in FIG. 8.

The thin film 820 is preferably patterned and etched to form at least one opening therein, such that xenon difluoride (XeF), for example, can be passed through the opening₂) The release material is introduced into the interior of the package structure 800 to release the sacrificial layer850. The number and size of these openings depends on the desired release rate of the sacrificial layer 850. These openings can be located anywhere in the thin film 820. In certain embodiments, the sacrificial layer 850 and the sacrificial layer within the interferometric modulator (between the fixed and movable mirrors 16a, 16b, 14a, 14b) may be released simultaneously. In other embodiments, the sacrificial layer 850 is not removed at the same time as the sacrificial layer within the interferometric modulator, but rather the sacrificial layer 850 is removed prior to removing the sacrificial layer within the interferometric modulator.

The embodiment shown in fig. 11 shows an alternative release technique. Fig. 11 is a top view of an embodiment of the package structure 800 after the thin film 820 has been deposited and patterned, but before the sacrificial layer 850 is released. As shown in fig. 11, a sacrificial layer 850 is deposited and patterned to have a plurality of protrusions 855. Then, a thin film 820 is deposited on the sacrificial layer 850 and the transparent substrate 810. After the thin film 820 is deposited, it is then preferably etched back on each side, as shown in FIG. 11. The package structure 800 may then be exposed to a release material, such as xenon difluoride (XeF)₂) The release material first reacts with the exposed sacrificial layer 850 material and then enters the package structure 800 through openings formed at the ledges 855 by removing the sacrificial layer 850 on each side of the package structure 800. It will be appreciated that the number and size of the projections 855 will depend on the desired release rate of the sacrificial layer 850.

To remove a sacrificial layer formed of molybdenum (Mo), silicon (Si), tungsten (W), or titanium (Ti), xenon difluoride (XeF) can be introduced through one or more openings in the thin film 820₂) Into the interior of the package structure 800. These openings in thin film 820 are preferably formed by etching openings in thin film 820. Xenon difluoride (XeF)₂) Reacts with the sacrificial layer 850 to remove the sacrificial layer 850, leaving a cavity 840 between the interferometric modulator 830 and the thin film 820. After the thin film 820 has been deposited, the sacrificial layer 850, which is formed of spin-on glass or oxide, is preferably gas etched or vapor etched to remove the sacrificial layer 850. Those skilled in the art will appreciate that the removal process will depend on the material of the sacrificial layer 850.

Those skilled in the art will also appreciate that it is desirable to have a cavity 840 behind the interferometric modulator 830 to enable the mechanical components of the interferometric modulator 830, such as the movable mirrors 14a, 14b, to be free to move. The height h of the cavity 840 formed depends on the thickness of the sacrificial layer 850.

In certain embodiments, the thin film 820 may be any type of material that is hermetic or hydrophobic, including but not limited to nickel, aluminum, and other types of metals and foils. The thin film 820 may also be formed of an insulator including, but not limited to, silicon dioxide, aluminum oxide, or nitride.

Alternatively, the thin film 820 may be made of a non-hermetic material. Suitable non-hermetic materials include polymers such as, for example, PMMA, epoxy, and organic or inorganic spin-on-glass (SOG) type materials. If a non-hermetic material is used for the thin film 820, an overcoat layer 860 is preferably formed over the non-hermetic thin film as shown in FIG. 12 to provide additional protection for the interferometric modulator 830 after the sacrificial layer 850 is removed, as shown in FIG. 12. Such an overcoat layer 860 is preferably made of a moisture barrier and has a thickness of about 1000 angstroms to about 10,000 angstroms. In one embodiment, the overcoat layer 860 is Barix, a thin film coating commercially available from Vitex Systems, Inc. located in San Jose, Calif. Such an overcoat may be multilayered, where some layers may be used for hermetic applications and some layers may be used for mechanical applications as described below.

In some embodiments in which the thin film 820 is a hydrophobic material, it is not necessary to form a hermetic seal, but a conventional backplane may not be required. It will be appreciated that any further moisture barrier required may be incorporated in the next packaging step at the module level.

The thin film 820 may be deposited to a thickness of about 1 micron by Chemical Vapor Deposition (CVD) or other suitable deposition method. Those skilled in the art will appreciate that the thickness of the thin film 820 may depend on the particular material properties of the selected material of the thin film 820.

The thin film 820 may be either transparent or opaque. Since the image is displayed not through the thin film 820, but through the transparent substrate 810, it is to be understood that the thin film 820 need not be transparent. It will be appreciated by those skilled in the art that the thin film 820 can be formed using transparent materials such as spin-on glass, as their material properties can be suitable for use as the thin film 820 to protect the interferometric modulator 830. For example, a transparent material such as spin-on glass may provide greater strength and protection to the interferometric modulator 830 within the package structure 800.

After the sacrificial layer 850 is released, the openings in the thin film 820 are preferably sealed. In one embodiment, epoxy is used to seal the openings. Those skilled in the art will appreciate that other materials may be used and it is preferred to use a material having a high viscosity. If the openings are small enough (e.g., less than 1 μ), another layer of thin film 820 material may be used to seal the openings.

In some embodiments, including but not limited to some embodiments having a hermetic thin film 820, an overcoat layer 860 may be deposited on the thin film 820 after the sacrificial layer 850 has been removed, as shown in FIG. 12. The outer coating is preferably formed of a polymer and preferably has a thickness of about 1 micron to several millimeters. The overcoat layer 860 may provide additional strength and stiffness to the thin film 820. In some embodiments where the thin film 820 is sufficiently small (e.g., less than 1 μ), the overcoat layer 860 may be used to seal these openings instead of another layer of the thin film 820 as described above.

As shown in fig. 7, the thin film 820 preferably hermetically seals the interior of the package structure 800 from the surrounding environment. Since the thin film 820 may provide a hermetic seal, the use of a desiccant is not required because the hermetic seal may prevent moisture from entering the package structure 800 from the surrounding environment. In another embodiment, the thin film 820 provides a semi-hermetic seal and a desiccant is included in the package structure 800 to absorb excess moisture.

A desiccant may be used to control moisture resident within the package structure 800. However, because the thin film 820 may provide a hermetic seal-depending on the material selected, a desiccant is not required to prevent moisture from entering the interior of the package structure 800 from the atmosphere. In the case of a semi-hermetic thin film 820, the amount of desiccant required can be reduced.

In one embodiment, the method of packaging an interferometric modulator according to the present embodiment integrates the sealing of the package structure 800 into the front end processing without the use of a separate backplane, desiccant, and seal, thereby reducing the cost of the package. In another embodiment, the thin film 820 reduces the amount of desiccant required rather than eliminating the need for a desiccant. Packaging according to these embodiments reduces material constraints on both the desiccant and the seal, allowing for a greater choice or materials, geometries, and opportunities to reduce costs. The thin film 820 may reduce the hermetic requirements so that not only can the backplane be eliminated but any additional moisture barrier requirements can be incorporated into the module level package. It is generally desirable to make the package as thin as possible, thus making the package 800 of fig. 7 provide a thin structure.

The package structure 800 is able to be thinner because no desiccant is needed. Typically, in packages containing desiccants, the expected lifetime of the device may depend on the lifetime of the desiccant. When the desiccant is completely consumed, the interferometric modulator display will fail as sufficient moisture enters the package structure to damage the interferometric modulator. The theoretical maximum lifetime of the device depends on the water vapor flux into the package and the amount and type of desiccant. In the package structure 800, the interferometric modulator 830 will not fail due to the depletion of the desiccant because the package structure 800 of the present embodiment does not contain any desiccant.

In another embodiment, the thin film 820 is not hermetic, but is permeable to xenon difluoride (XeF)₂) Or another removal gas, xenon difluoride (XeF)₂) Or another mobile gas, will react with the sacrificial layer 850 to remove the sacrificial layer 850, thereby leaving a cavity 840 between the interferometric modulator 830 and the thin film 820. According to the present embodiment, some suitable materials for the thin film 820 include, but are not limited to, porous alumina and some aerogels. In the present embodiment, the thin film 820 need not be formed with any openingsAs long as it is permeable to xenon difluoride (XeF)₂) Or another removal gas. Preferably, after the sacrificial layer 850 is removed, a hermetic overcoat 860 is deposited over the thin film 820 to hermetically seal the package structure 800. In these embodiments, the overcoat layer 860 is preferably formed of a metal.

FIGS. 13A and 13B are system block diagrams illustrating one embodiment of a display device 2040. The display device 2040 can be, for example, a cellular or mobile telephone. However, the same components of display device 2040 and slight variations thereof are also illustrative of various types of display devices such as televisions and portable media players.

The display device 2040 includes a housing 2041, a display 2030, an antenna 2043, a speaker 2045, an input device 2048, and a microphone 2046. The housing 2041 is typically made by any of a number of manufacturing processes well known to those skilled in the art, including injection molding and vacuum forming. Further, the housing 2041 may be made from any of a wide variety of materials, including but not limited to plastic, metal, glass, rubber, and ceramic, or a combination thereof. In one embodiment, the housing 2041 includes removable portions (not shown) that can be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols.

The display 2030 of exemplary display device 2040 may be any of a wide variety of displays, including a bi-stable display as described herein. In other embodiments, the display 2030 includes a flat panel display, such as a plasma display, EL, OLED, STN LCD, or TFT LCD as described above, or a non-flat panel display, such as a CRT or other tube device, as is well known to those of skill in the art. However, for purposes of describing the present embodiment, the display 2030 includes an interferometric modulator display, as described herein.

FIG. 13B schematically shows components in an embodiment of an exemplary display device 2040. The exemplary display device 2040 shown includes a housing 2041 and may include other components at least partially enclosed therein. For example, in one embodiment, the exemplary display device 2040 includes a network interface 2027, the network interface 2027 including an antenna 2043 coupled to a transceiver 2047. The transceiver 2047 is connected to the processor 2021, which processor 2021 is in turn connected to conditioning hardware 2052. Conditioning hardware 2052 may be configured to condition (e.g., filter) a signal. Conditioning hardware 2052 is coupled to a speaker 2045 and a microphone 2046. The processor 2021 is also connected to an input device 2048 and a driver controller 2029. The driver controller 2029 is coupled to a frame buffer 2028 and to the array driver 2022, which in turn is coupled to a display array 2030. A power supply 2050 provides power to all components as required by the design of the particular exemplary display device 2040.

The network interface 2027 includes the antenna 2043 and the transceiver 2047 so that the exemplary display device 2040 can communicate with one or more devices over a network. In one embodiment, the network interface 2027 may also have some processing functions to reduce the requirements on the processor 2021. The antenna 2043 is any antenna known to those skilled in the art for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE802.11 standard, including IEEE802.11 (a), (b), or (g). In another embodiment, the antenna transmits and receives RF signals according to the Bluetooth (BLUETOOTH) standard. In the case of a cellular telephone, the antenna is designed to receive CDMA, GSM, AMPS or other known signals that are used to communicate within a wireless mobile telephone network. The transceiver 2047 pre-processes the signals received from the antenna 2043 so that they may be received by and further processed by the processor 2021. The transceiver 2047 also processes signals received from the processor 2021 so that they may be transmitted from the exemplary display device 2040 via the antenna 2043.

In an alternative embodiment, the transceiver 2047 may be replaced by a receiver. In yet another alternative embodiment, the network interface 2027 can be replaced by an image source, which can store or generate image data to be sent to the processor 2021. For example, the image source can be a Digital Video Disc (DVD) or a hard-disc drive that contains image data, or a software module that generates image data.

The processor 2021 generally controls the overall operation of the exemplary display device 2040. The processor 2021 receives data, such as compressed image data, from the network interface 2027 or an image source and processes the data into raw image data or into a format that is readily processed into raw image data. The processor 2021 then sends the processed data to the driver controller 2029 or to frame buffer 2028 for storage. Raw data generally refers to information that can identify the image characteristics at each location within an image. For example, the image characteristics may include color, saturation, and gray-scale level.

In one embodiment, the processor 2021 includes a microcontroller, CPU, or logic unit to control operation of the exemplary display device 2040. Conditioning hardware 2052 typically includes amplifiers and filters for transmitting signals to the speaker 2045, and for receiving signals from the microphone 2046. Conditioning hardware 2052 may be discrete components within the exemplary display device 2040 or may be incorporated within the processor 2021 or other components.

The driver controller 2029 receives raw image data generated by the processor 2021 either directly from the processor 2021 or from the frame buffer 2028 and reformats the raw image data appropriately for high speed transmission to the array driver 2022. In particular, the driver controller 2029 reformats the raw image data into a data flow having a raster-like format, such that it has a time order suitable for scanning the display array 2030. The driver controller 2029 then sends the formatted information to the array driver 2022. Although a driver controller 2029, such as an LCD controller, is typically associated with the system processor 2021 as a stand-alone Integrated Circuit (IC), such controllers may be implemented in a number of ways. They may be embedded in the processor 2021 as hardware, embedded in the processor 2021 as software, or fully integrated in hardware with the array driver 2022.

Typically, the array driver 2022 receives the formatted information from the driver controller 2029 and reformats the video data into a parallel set of waveforms that are applied many times per second to the hundreds and sometimes thousands of leads coming from the display's x-y matrix of pixels.

In one embodiment, the driver controller 2029, array driver 2022, and display array 2030 are appropriate for any of the types of displays described herein. For example, in one embodiment, the driver controller 2029 is a conventional display controller or a bi-stable display controller (e.g., an interferometric modulator controller). In another embodiment, the array driver 2022 is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, a driver controller 2029 is integrated with the array driver 2022. Such embodiments are common in highly integrated systems such as cellular phones, watches, and other small area displays. In yet another embodiment, the display array 2030 is a typical display array or a bi-stable display array (e.g., a display including an array of interferometric modulators).

The input device 2048 enables a user to control the operation of the exemplary display device 2040. In one embodiment, input device 2048 comprises a keypad (e.g., a QWERTY keyboard or a telephone keypad), a button, a switch, a touch-sensitive screen, a pressure-or heat-sensitive membrane. In one embodiment, the microphone 2046 is an input device for the exemplary display device 2040. When the microphone 2046 is used to input data to the device, voice commands may be provided by a user to control operation of the exemplary display device 2040.

The power supply 2050 can include a wide variety of energy storage devices, as are well known in the art. For example, in one embodiment, power supply 2050 is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, power supply 2050 is a renewable energy source, a capacitor, or a solar cell, including plastic solar cells and solar-cell paint. In another embodiment, power supply 2050 is configured to receive power from a wall outlet.

In some implementations control programmability resides, as described above, in a driver controller, which can be located in several places in the electronic display system. In some cases, control programmability exists in the array driver 2022. Those skilled in the art will appreciate that the above-described optimization may be implemented in any number of hardware and/or software components and in various configurations.

While there have been shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. It will be understood that the present invention may be embodied within a form that does not provide all of the features and advantages described herein, as some features may be used or practiced separately from others.

Claims (38)

1. A display device comprising an array of movable mirrors configured for interferometric modulation of light, the display device comprising:

a transparent substrate;

an interferometric modulator comprising the array of movable mirrors, and wherein the interferometric modulator is configured to modulate light transmitted through the transparent substrate; and

a deposited freestanding thin film back plate that encapsulates the array of movable mirrors within a package between the transparent substrate and the deposited freestanding thin film back plate, and wherein a gap exists between the entire array of movable mirrors and the deposited freestanding thin film back plate.

2. The display device of claim 1, wherein the gap is formed by removing a sacrificial layer between the movable mirror array and the deposited free-standing thin film backplate.

3. The display device of claim 1, wherein the deposited free-standing thin film backplane comprises a hermetic material.

4. The display device of claim 1, wherein the deposited free-standing film is nickel.

5. The display device of claim 1, wherein the deposited free-standing film is aluminum.

6. The display device of claim 1, further comprising:

a processor in electrical communication with the movable mirror array, the processor configured to process image data; and

a memory device in electrical communication with the processor.

7. The display device of claim 6, further comprising:

a drive circuit configured to send at least one signal to the movable mirror array.

8. The display device of claim 7, further comprising:

a controller configured to send at least a portion of the image data to the drive circuit.

9. The display device of claim 6, further comprising:

an image source module configured to send the image data to the processor.

10. The display device of claim 9, wherein the image source module comprises at least one of a receiver, transceiver, and transmitter.

11. The display device of claim 6, further comprising:

an input device configured to receive input data and to communicate the input data to the processor.

12. The display device of claim 1, wherein the display device comprises a cellular telephone.

13. A method of manufacturing a display device comprising an array of movable mirrors configured for interferometric modulation of light, the method comprising:

providing a transparent substrate;

forming an interferometric modulator on the transparent substrate, wherein the interferometric modulator comprises the array of movable mirrors; and

depositing a free-standing thin film backplate over the movable mirror array and the transparent substrate to seal the movable mirror array between the transparent substrate and the free-standing thin film backplate, wherein a gap exists between the entire array of movable mirrors and the free-standing thin film backplate.

14. The method of claim 13, further comprising:

depositing a sacrificial layer over the interferometric modulator prior to depositing the free-standing thin film backplane; and

after depositing the free-standing thin film backplate, the sacrificial layer is removed so as to provide the gap between the interferometric modulator and the free-standing thin film backplate.

15. The method of claim 14, further comprising patterning the free-standing thin film backplane to form at least one opening in the free-standing thin film backplane.

16. The method of claim 14, further comprising patterning the free-standing thin film backplane to expose a portion of the sacrificial layer.

17. The method of claim 13, wherein the free-standing thin film backplane is formed of aluminum.

18. The method of claim 13, wherein the free-standing thin film backplane is formed of nickel.

19. The method of claim 13, wherein the free-standing thin film backplane is formed from spin-on glass.

20. The method of claim 13, wherein the freestanding thin film backplane is formed from a hermetic material.

21. The method of claim 14, wherein the sacrificial layer is formed of spin-on-glass.

22. A mems display device comprising a movable mirror array configured for interferometric modulation of light, the mems display device comprising:

a transparent substrate;

an interferometric modulator formed on the transparent substrate, the interferometric modulator comprising the array of movable mirrors; and

a deposited freestanding thin film back plate sealed to the transparent substrate to encapsulate the array of movable mirrors between the transparent substrate and the deposited freestanding thin film back plate, wherein a cavity exists between the entire array of movable mirrors and the deposited freestanding thin film back plate.

23. The mems display device of claim 22, wherein the cavity is formed by removing a sacrificial layer between the movable mirror array and the deposited free-standing thin film backplate.

24. The mems display device of claim 22, wherein the cavity allows movement of one or more movable mirrors in the array of movable mirrors.

25. The mems display device of claim 22, wherein the deposited free-standing thin film backplane comprises a hermetic material.

26. The mems display device of claim 22, further comprising an overcoat layer deposited on the deposited free-standing thin film backplane.

27. The mems display device of claim 26, wherein the overcoat layer comprises a moisture resistant material.

28. The mems display device of claim 26, wherein the overcoat comprises a polymer.

29. The mems display device of claim 22, wherein the deposited free-standing thin film backplane comprises a metal.

30. The mems display device of claim 22, wherein the deposited free-standing thin film backplane comprises a polymer.

31. A display device comprising an array of movable mirrors configured for interferometric modulation of light, the display device comprising:

a transparent substrate;

an interferometric modulator comprising the array of movable mirrors, wherein the interferometric modulator is configured to modulate light transmitted through the transparent substrate, and wherein the interferometric modulator is formed on the transparent substrate;

a free-standing thin film back plate deposited over the movable mirror array, wherein the free-standing thin film back plate seals the movable mirror array within a package between the transparent substrate and the free-standing thin film back plate; and

a cavity between the entire array of movable mirrors and the free-standing thin film backplate, wherein the cavity is formed by removing a sacrificial material.

32. The display device of claim 31, wherein the free-standing thin film backplane is air-tight.

33. The display device of claim 31, wherein the free-standing thin film backplane is a metal.

34. The display device of claim 31, wherein the free-standing thin film backplane is a polymer.

35. A display device, comprising:

a transmission member for transmitting light therethrough;

a modulating means configured to modulate light transmitted through said transmitting means, wherein said modulating means comprises an array of movable mirrors; and

a sealing member for sealing the movable mirror array in a package between the transmissive member and the sealing member, wherein the sealing member comprises a deposited free-standing film, and wherein a cavity exists between the entire array of movable mirrors and the sealing member.

36. The display device of claim 35, wherein the cavity is formed by removing a sacrificial layer between the movable mirror array and the sealing member.

37. The display device according to claim 35, wherein the sealing member contains a gas-tight material.

38. The display device of claim 35, wherein the deposited thin film is permeable to xenon difluoride and the sealing means further comprises a hermetic material formed on the deposited freestanding thin film.