JP4431196B2 - Interferometric modulation - Google Patents

Description

Background The present invention is a continuation-in-part of US patent application Ser. No. 08 / 238,750 filed May 5, 1994, which is incorporated by reference.
The present invention relates to visible spectrum (including ultraviolet and infrared) modulator arrays.
The parent application describes two types of structures in which their impedance, ie the inverse of admittance, is actively adjusted so that they can modulate light. One way is a deformable cavity whose optical properties can be changed by electrostatic deformation of one of the cavity walls. Depending on the composition and thickness of these walls of dielectric, semiconductor or metal film layers, various modulator designs can be made that exhibit different optical responses to the applied voltage.
One such design includes a filter described as a hybrid filter having a narrow band filter and an induced absorber. When the wall associated with the hybrid filter contacts the reflector, a certain range of incident light is absorbed. This occurs because the stimulated absorber matches the impedance of the reflector with that of the incident medium for frequencies in the range that passes through the narrowband filter.
Overview The present invention eliminates the need for narrowband filters and provides a broader absorption range.
The present invention modulates light by electrostatically changing the spacing of a cavity with two walls, one of which is a reflector and the other is a guide absorber. This cavity is constructed on an optically smooth surface, i.e. a surface that is sufficiently smooth to produce interference effects.
Accordingly, in one aspect, the invention generally features an interferometric modulator cavity having a reflector and an induced absorber.
Implementations of the invention may include one or more of the following features. The reflector may include a film made of metal, dielectric, semiconductor, or a combination thereof. The induced absorber may include an absorber sandwiched between two matching layers. One of the matching layers can be located at the boundary of the absorber with the incident medium, and the other matching layer can be located at the boundary of the absorber with the reflector. At least one of the matching layers can include a metal film. At least one of the matching layers can include a derivative film or a semiconductor film, or a combination of at least two metal films, a dielectric film, or a semiconductor film. The absorber can include a high loss film such as a metal or a high loss film such as a semiconductor, or a combination of a metal and a semiconductor film. There may also be a substrate containing a transparent incident medium. Stimulated absorbers and / or reflectors can also be present on the substrate. The substrate may be transparent and may function as an incident medium or an opaque body in some cases. The spacer may be air or any other flexible medium (eg, liquid or synthetic resin) that can change the thickness of the gap.
In general, in another aspect, the invention features a direct view reflective flat panel display with an interferometric modulator array.
Implementations of the invention may include one or more of the following features. The array can include multiple sets of interferometric modulators, each set arranged such that pairs of different reflection states are switched. The array can also include a set of interferometric modulators whose sets are arranged to be driven analogly to reflect any particular color. The brightness of each modulator is controlled by pulse width modulation, spatial dithering, or a combination of the two. The array may be sealed by a backplane. The backplane may include an integral element. The backplane may be bonded. The backplane may support electrodes that modify the electromechanical response of the pixel. Each modulator can also be moved by electrostatic force, piezoelectric force or magnetic force. The display may be used in a projection system. To reduce or eliminate color shifts depending on viewing angle, to provide auxiliary front lighting, or to reduce or eliminate color shifts depending on viewing angle A compensation mechanism may be used. The substrate may be an integrated circuit.
In general, in another aspect, the present invention uses a lift-off technique to form a pattern of spacers that are deposited separately, with different thickness spacers for each deposit. Features a method for constructing adjacent spacers of varying thickness on a substrate, as provided. Alternatively, a patterned photoresist may be used to enable etching to selectively etch away the thickness of the spacer deposited in a single deposition. .
In general, in another aspect, the invention features a full color still image comprising an array of interferometric modulator cavities. Each cavity includes a reflector and an induced absorber, and the absorbing derivative includes a spacer having a thickness that defines a color associated with the cavity.
In general, in another aspect, the present invention provides an image obtained by combining all the patterns with one thickness such that in each pattern the spacer defines one color associated with that pattern. Features a full-color still image comprising a separate pattern of spacers, or interferometric modulator cavities with spacers.
The advantages of the invention are believed to be one or more of the following. By using pixels based on these new cavities, it will be possible to produce high quality full color flat panel displays. By combining three sets of these pixels designed to switch between red and black, green and black, and blue and black, respectively, by configuring pixels that can switch between two colors (eg red and black) It seems that a flat panel display can be constructed. The inherent color eliminates the need for a color filter array typically required for color LCDs. Furthermore, a reflective display that uses room light instead of backlighting is particularly susceptible to the inefficiency of pixels. The cavity of the present invention makes use of over 90% of the incident light and is an excellent candidate for this application. In addition, these structures also exhibit microelectromechanical hysteresis when driven electrostatically, and this can be used to eliminate the need for transistors.
Other advantages and features of the invention will be apparent from the following description and from the claims.
Description FIG. 1 is a diagram of each layer of a modulator.
FIG. 2 is a perspective view of a cavity in the apparatus.
FIG. 3 is a side view of the pixel device.
FIG. 4 is a graph of optical response for a cavity with a black appearance.
FIG. 5 is a graph of optical response for a cavity having a blue appearance.
FIG. 6 is a graph of optical response for a cavity having a green appearance.
FIG. 7 is a graph of optical response for a cavity having a red appearance.
FIG. 8 is a graph of optical response for a cavity having a white appearance.
FIG. 9 is a perspective view of a fragment of a reflective flat panel display.
Figures 10a, 10b, 10c, 10d are perspective views of various spacers during fabrication.
FIGS. 11a, 11b, 11c, 11d are also perspective views of various spacers being fabricated.
12a, 12b, 12c, and 12d are overhead views of still images.
Any thin film, medium or substrate (think of a thin film) can be defined in terms of intrinsic optical admittance. By considering only the reflectivity, the operation of the thin film can be examined by treating it as an admittance converter. That is, the specific admittance of another thin film or substrate (converted film) deposited thereon can be changed by the thin film or combination of thin films (converter). In this manner, a film or substrate that is normally reflective changes its intrinsic admittance so that its reflectivity is enhanced and / or decreased upon deposition or contact with the transducer (ie, converted). )it is conceivable that. In general, reflections always occur at the interface of any combination of film, medium or substrate. The closer these two admittances are, the lower the reflectance at the interface between the two is. If the admittances match, the reflectance is zero.
Referring to FIG. 1, a reflector 100 (converted film) is separated from a stimulated absorber 105 (converter) that includes films 104, 106 and 108 by a variable thickness spacer. The incident medium 110 has the other side of the induction absorber 105 as a boundary. Each of these thin films has been microfabricated in the manner described in the parent patent application. The induced absorber 105 performs two functions. The first function is to match the admittance of the reflector 100 and the incident medium 110. This is through the matching layer 108 used to convert the admittance of the absorber 106 to that of the incident medium 110, and the matching layer 104 used to convert the admittance of the reflector 100 to that of the absorbing medium 106. Achieved. The second function is light absorption. This is accomplished using an absorber 106 that functions to attenuate light incident from the reflector 100 in addition to light incident through the medium.
Since the thickness T of the spacer 102 can be changed, the optical characteristics of the entire structure can be modified. Referring to FIG. 2, the pixel 200 indicates a driving state, and the pixel 202 indicates a non-driving state. In this case, the inductive absorber 206 (converter) is present on the substrate 204, and the reflector 208 (converted film) is a self-supporting structure. When a voltage is applied, the reflector 208 comes into contact with or near the induction absorber 206. By selecting the appropriate material and thickness, the admittance of the reflector 208 will be completely converted to that of the substrate 204. As a result, it is considered that the light 205 having a certain wavelength incident through the substrate 204 is significantly absorbed by the pixel. When no voltage is applied, the reflector 208 returns to its normal structure, which changes the relative admittance of the reflector and the substrate. In this state (pixel 202), the cavity behaves closer to the resonant reflector, reflecting a certain range of frequencies strongly, but otherwise highly absorbing.
For this reason, by selecting an appropriate material, any color (or a combination of multiple colors) can be absorbed from a state of reflecting (for example, blue to black), or any combination of colors can be arbitrarily reflected. A pixel that can be switched to a state of reflecting other colors (for example, white to red) can be configured. Referring to FIG. 3, in a special pixel design, the substrate 402 is made of glass, the matching layer 404 is a 54.46 nm thick zirconium dioxide film, and the absorber 406 is a 14.49 nm thick tungsten film. The layer 408 is a 50 nm thick silicon dioxide film, the spacer 400 is air, and the reflector 410 is a silver film having a thickness of at least 50 nm. Referring to FIG. 4, the photoresponse of a pixel in the driven state is shown, i.e., a stimulated absorption state occurs over a wide range when the reflector 410 is in contact with a matching layer 408. Referring to FIGS. 5-8, differently colored pixels are shown, each corresponding to the reflection of blue, green, red and white light, all in the undriven state. These responses correspond to 325, 435, 230 and 700 nm, respectively, with the thickness of the non-driven spacer.
Referring to FIG. 9, the cross section of the full-color reflective flat panel display 298 includes three types of R, G, and B pixels. The only difference between each type is the size of the non-actuated spacer, which is determined during manufacture as described in the parent patent application. The induced absorber 300 is present on the substrate 304 and the reflector 308 is self-supporting. It is sealed by an integrated back plate 302 that can be composed of a thick organic or inorganic film. Alternatively, the pack plate can be composed of separate pieces such as glass that are arranged and bonded to the substrate. Electrodes may be present on this backplate so that the electromechanical capabilities of the pixel are modified. Incident light 310 propagates through optical compensation mechanism 306 and substrate 304 where it is selectively reflected or absorbed by the pixels. The display may be controlled or driven by a circuit of the type described in the parent application.
In this display, the optical compensation mechanism 306 performs two functions. The first function is to reduce or eliminate the shift that occurs in the reflected color depending on the incident angle. This is a feature of all interference films and can be compensated by using films with specially tuned reflection indices or holographic properties, or films with micro-optics. Other methods are also possible. The second function is to provide an auxiliary front lighting source. This method allows additional light to be added to the front of the display when room lighting conditions are significantly reduced, thereby allowing the display to operate in conditions ranging from high brightness to full black. It becomes possible. Such a front light can be configured using a patterned organic light emitter or an edge lighting light source connected to a micro optical array inside an optical compensation film. Other methods are also possible.
A general method for configuring the device is described in the parent application. Further details of two alternative methods for constructing various different sized spacers are as follows, but other methods are also possible.
Both alternative methods include repetitive deposition and patterning of an antiseptic spacer material that is removed by etching to form air gaps at the final stage of the larger method.
Referring to FIG. 10a, a substrate 1000 is shown with an induced absorber 1002 already deposited and a photoresist 1004 that has been deposited and patterned. Induced absorber 1002 is deposited using any number of techniques for thin film deposition such as sputtering, electron beam evaporation and the like. The photoresist is applied by spinning and is patterned by overexposure to obtain natural protrusions, thereby creating a stencil. The result is that, using a procedure known as lift-off, it can be used to pattern a subsequently deposited material. Referring to FIG. 10b, spacer material 1006 has been applied, resulting in extra spacer material 1008 on top of the stencil. Referring to FIG. 10c, the stencil is lifted off with excess spacer material by immersing the device in a solvent bath such as acetone and stirring with ultrasound. Referring to FIG. 10d, the above method is reinitiated with the new photoresist 1010 patterned and deposited in such a way that a new spacer 1012 is deposited adjacent to the old spacer 1006. Yes. By repeating this method once more, three types of spacers having different thicknesses are obtained. Referring to FIG. 10d, the above method using a new photoresist 1010 patterned and deposited in such a way that a new spacer 1012 having a different thickness is deposited adjacent to the old spacer 1006. Has started again.
Referring to FIG. 11a, a substrate 1000 is shown with an induced absorber 1102 already deposited. Spacer materials 1104, 1106, and 1108 are also deposited and patterned with a lift-off stencil 1110. The spacer material has a thickness corresponding to the maximum of the three types of thickness required for the pixel. Referring to FIG. 11b, a new photoresist 1112 is deposited and patterned so that the stencil is lifted off with excess material, leaving the spacer 1104 exposed. Referring to FIG. 11c, the spacer material 1104 has been scraped by etching by one of many techniques including wet chemical etching and reactive ion etching. Only part of the necessary spacer material is removed by etching, and the rest is etched in the subsequent etching steps. Photoresist 1112 is subsequently removed using similar techniques. Referring to FIG. 11d, a new photoresist 1114 has been deposited and patterned to expose the spacers 1104 and 1106. FIG. All the etching of the spacer 1106 is performed at this stage, and the etching of the spacer 1104 is completed. The photoresist 1114 is then removed and the process is complete.
Other embodiments are within the scope of the following claims.
For example, the spacer material need not be finally removed and may remain as part of the completed device. In this manner, any pattern may be constructed in place of a simple array of pixels by further using previously described pattern shaping techniques. For this reason, a full-color still image can be drawn by a method similar to the conventional printing method. In conventional printing, an image is separated into a number of different colors to be presented, namely a plurality of colors that are essentially a subset of the monochromatic image of the image: red separation, blue separation, green separation and black separation. A full color image is created by printing each separation using different color inks in the same area.
Alternatively, in the method we name “Iridescent Printing”, the different separations include multiple layers of thin film corresponding to the IMod design described herein and in the referenced patent. A vivid full-color image can be obtained by patterning, printing, or separating a combination of a plurality of colors in the same region.
Referring to FIG. 12a, a rectangular substrate is shown with a region 1200 showing a portion of the substrate patterned with a thin film stack optimized for black. Referring to FIG. 12b, the substrate is subsequently patterned in region 1202 with a thin film stack optimized for red. Referring to FIG. 12c, the substrate is subsequently patterned in region 1204 with a thin film stack optimized for green. Referring to FIG. 12d, the substrate is subsequently patterned in region 1206 with a thin film stack optimized for blue.
Or a simpler method can be obtained if it is assumed that only the design of the inductive absorber is used. In this method, the entire substrate is first coated with a stack of induced absorbers. Subsequent steps are then performed to pattern only the spacer material using the technique described above. After the desired spacer, i.e. the color, has been defined, a final deposition of the reflector is performed.
The brightness of different colors can be changed by changing the amount of black interspersed within a particular color, ie spatial dithering. The image also exhibits a pleasant color shift known as iridescent depending on the viewing angle.
In another example, a reflective flat panel display can be constructed using one type of pixel instead of three types of pixels. In this case, multiple colors can be obtained by constructing a continuously adjustable type of pixel or analog interferometric modulator as described in the parent patent application. In this manner, any individual pixel can be adjusted to reflect any particular color by applying an appropriate voltage. This requires that the array be configured with electrical circuitry on the substrate or directly on the surface of the integrated circuit in order to provide a charge storage mechanism. Although this method requires a more complicated driving method corresponding to the analog voltage, it provides better resolution. This is also considered to have application in the projection system.

Claims (17)

An interferometric modulator comprising a reflector configurable to move from a first position to a second position , a medium that receives incident light, and a first absorber located between the reflector and the medium And when the reflector is in the first position, the admittance of the reflector is adjusted so that the first absorber is less reflective at the interface between the first absorber and the reflector. The admittance of the reflector is substantially matched to the admittance so that when the reflector is in the second position, the first absorber is more reflective at the interface between the first absorber and the reflector. Is an interferometric modulator that does not substantially match the admittance of the medium. The interferometric modulator of claim 1, wherein the reflector comprises a metal film. The interferometric modulator of claim 1, wherein the reflector includes a dielectric film. The interferometric modulator of claim 1, wherein the reflector includes a semiconductor film. 2. The interferometric modulator according to claim 1, wherein the reflector includes a combination of at least two of a metal film, a dielectric film, and a semiconductor film. The first absorber includes an absorber film, which is used to convert the admittance of the absorber film to the admittance of the reflector and the layer used to convert the admittance of the absorber film to the admittance of the medium interferometric modulators that are sandwiched claim 1, wherein between the layers used. One of the layers is located in the boundary portion of the absorber film and the medium, the other layers are located in the boundary portion of the reflector and the absorber film, interferometric modulator of claim 6 wherein. The interferometric modulator of claim 6, wherein at least one of the layers comprises a metal film. The interferometric modulator of claim 6, wherein at least one of the layers comprises a derivative film. The interferometric modulator of claim 6, wherein at least one of the layers comprises a semiconductor film. At least one of the layers is a metal layer, comprising at least two combination of the dielectric film and the semiconductor film, interferometric modulator of claim 6 wherein. 7. The interferometric modulator according to claim 6, wherein the absorber film includes a metal. 7. The interferometric modulator according to claim 6, wherein the absorber film includes a semiconductor. The interferometric modulator of claim 6, wherein the absorber film comprises a combination of metal and semiconductor films. The primary absorbent body, the first layer further including match at least a portion the absorber layer and the reflector admittance of medium admittance to absorb light, interferometric modulator of claim 1. The primary absorbent member further comprises a second layer to match at least a portion of the admittance of the reflector and admittance of the medium, interferometric modulator of claim 15, wherein. Absorber layer is disposed between the first and second layers, interferometric modulator of claim 16.

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