HK40004406B - Polarized light emission from micro-pixel displays and methods of fabrication thereof - Google Patents

Description

Polarized light emission from micro-pixel displays and methods of making the same

Cross Reference to Related Applications

This application claims the benefit of U.S. provisional patent application No. 62/429,033 filed on 1/12/2016.

Background

1. Technical Field

The present invention relates to solid state light emitters such as LED and laser diode structures. More particularly, the present invention relates to solid state light emitting structures made from group III nitride materials that utilize the unique crystallographic properties of the group III nitride materials, thereby emitting polarized light from the light emitting structure.

2. Prior Art

Solid state light emitters are at the forefront of today's commercial electronic display systems. Many display systems exploit the property of light polarization to obtain increased contrast between "on" and "off" pixels on a display element. The use of unpolarized light requires that such display systems include multiple polarizers and polarizing optics, which makes them larger, more complex, less energy efficient and more costly. III-nitride material systems provide a way to crystallographically tailor the polarization state of emitted light from group III-nitride materials by selecting crystal planes in the material that favor certain polarization states. This in turn allows the solid state lighting system to be manufactured with a minimal amount of lighting engineering, which inherently makes the system more efficient in terms of power consumption and design.

Some commercially available LEDs utilize group III nitride material systems. AlGaInN material systems (whose large band gap ranges from deep ultraviolet to near infrared emission wavelengths) are attractive systems for electronic displays because their output covers the entire visible electromagnetic spectrum. Most GaN LEDs used with existing display technologies are grown on the polar (0001) c-plane of wurtzite GaN. However, the non-basal plane of GaN provides a contrast to conventionalcThe distinctive advantages and different optical properties of planar GaN. Is undesirable due to use forcPolarization dependent electric fields, Quantum Confined Stark Effect (QCSE) inside the multiple Quantum wells of planar GaN lead to lower energy recombination transitions and characteristic blue shifts of the peak emission wavelength are observed as current density increases (t. Takeuchi, s. Sota, m. Katsuragawa, m. Komori, h. Takeuchi, h. Amano and i. Akasaki, "Quantum-confined starter effect to piezoelectric fields in GaInN strained Quantum" japanese applied physics report 36, 382 ion 385 line (1997)). Another undesirable consequence of c-plane growth is the efficiency drop that occurs at higher current densities (y.c. Shen, g.o. Mueller, s. Watanabe, n.f. Gardner, a. Munkholm and m.r. Krames, "Auger registration in InGaN measured by phosphor", applied physical prompter, 91, 141101 (2007)).

In 2000, "Nitride semiconductors from of electronic fields for electronic white light-emitting diodes", Nature 406, 865 (2000) reported on GaN by P.Walteriet, O.Brandt, A.Trampert, H.T.Grahn, J.Menniger, M.Ramsteiner, M.Reiche and K.H.ploogmOne of the first high quality non-polar growth materials on a plane. Nonpolar plane of GaN andcthe planes form an angle of 90 DEG, and the semipolar planes form an angle of 0 DEG andan intermediate angle between 90 deg.. The semipolar plane also having a non-zero valueh，kOriIndices and those planes that are non-zero/indexed in the Miller-Bravis indexing convention. Various crystal planes of the hexagonal GaN crystalline material are shown in fig. 1, including polar, non-polar and semi-polar planes.

And a substrate in GaNcThe planes are different, the non-polar and semi-polar planes show unequal photon emission, depending on the direction of the electric vector, i.e.: is perpendicular toAnd is parallel toIn thatcThe intensity of the light of the axes is unequal. Physical reviews using "k-p method for strained wurtzite semiconductors" from S, L Chuang and CS ChangB54, 2491-2504 (1996), which gave effective mass Hamilton amounts including strained wurtzite semiconductors, J.B. Jeon, B.C. Lee, Yu. M. Sinencko, K.W. Kim and M.A. Littlejohn, physical reports of the application of "Strain effects on optical gain in wurtzite GaN", 82, 386-391 (1997) were able to lay the theoretical basis for the anisotropy of the optical gain of wurtzite GaN and indicate that this anisotropy is caused by the anisotropic valence band. They mathematically show that using the average momentum matrix element taken from the full 6 x 6 hamiltonian for the valence band, the valence band factor necessarily contributes to the anisotropy because they are unequal. The valence band of GaN is mainly composed of N2 pComposition of states at wave vector k = 0 (Point) having atoms in the center of the brillouin zonep _x Andp _y the characteristic valence bands are degenerate, andp _z at a lower energy, and therefore separates the valence band into two (called crystal field splitting,) Without examinationSpin-orbit interactions are considered. The spin-orbit interaction results in the formation of a magnetic resonance system havingp _x Andp _y the state of the feature is no longer degenerate and forms the basis forcPlanar oriented Heavy Hole (HH) and Light Hole (LH) bands. The band characteristics around the conduction band minimum are not affected by this type of splitting, since the states there are mainly composed of N and Ga, which are symmetric in all directionssAnd (4) track characteristic composition.

cThe wave function (ground state) of the valence band in the plane (taken in the xy plane) is physically reviewed by S.L Chuang and C.S. Chang in "k-p method for strained wurtzite semiconductorsB54, 2491-2504 (1996) is defined as:

from the above formula, it is clear that the HH and LH bands are () And in the presence of isotropic biaxial straincIn plane orientation (in which the strain component epsilon_xx = ε_yy) There is no optical polarization anisotropy. However, for non-polar and semi-polar crystal orientations, the strain is no longer isotropic. Using the m-plane as an example, the Analysis of polarization and amplification of the c axis in the phosphor luminescence center of the Wurtzite GaN in K.Donen, K.Horino, A.Kuramata and T.tanahashi, applied physical promulgation, 71, 1996-1998 (1997) has shown that the crystal field in GaN is strong enough to be fixed along the edge cOf shaftspThe axis of function. The original hybrid state in the c-plane orientation is no longer maintained and the state now becomes similar to that of the c-plane orientationAnd is similar toS, L Chuang and C.S. Chang "K-p method for strained wurtzite semiconductors ", physical reviewB,54, 2491-2504 (1996). Growth of InGaN/GaN wells (e.g. in a field-effect transistor with compression, biaxial, anisotropic)mIn-plane) strain energy in the z-direction (c-axis,state, which will be calledE _v3 ) It is now raised aboveThe status of the mobile station is,E _v2 . TheStatus of stateE _v1 Also from increased strain, but it is already higher than the other two states, so it retains its relative position as the topmost energy valence band anddue to the fact thatmThe tensile strain of the shaft decreases. A schematic diagram of this demonstration is illustrated in fig. 2.

When the growth of GaN is alongcElectric field component (E) when guided axially (z direction)_xAnd E_y) Will always be perpendicular tocAxes and as electrons radiatively transition to the valence band, there is no difference in their polarization states and thus the emitted light is uniformly unpolarized. However, when the growth of GaN is along the nonpolar or semipolar plane (again, in the same way as above)mPlane as an example), the electric field component E _zNow parallel tocA shaft, E_yPerpendicular tocShaft and aim atHas a higher probability of radiation transition andis more likeE _v1 （State) forHas a lower probability of radiation transition and is preferredE _v3 （Status). Thus, two different polarization states can now be obtained in the light emission. To physically quantify the amount of polarization in a sample, its polarization ratio ρ is defined as:

here, theIs provided withcThe intensity of light polarized with the axis perpendicular (parallel) and determines the limit of the maximum value of the contrast in display technology. Due to quantum confinementp _z The valence band states are mixed and the degree of polarization will always deviate from unity (B. Rau, P. Walteriet, O. Brandt, M. Ramsteiner, KH Ploog, J. Puls and F. Henneberger, "In-plane polarization and polarization of the polarization emission ofM-plane GaN/(Al,Ga)N quantum wells”，Application physical flash newspaper,77, 3343-3345(2000)). A more thorough discussion of this effect can be found in the Japanese applied Physics report of Y. ZHao, R.M. Farrell, Y. -R.Wu and J. Speck, "volume band stands and polarized optical emission from NONPolars and semi-polar III-nitride quantum well optical electronic devices," 53, 100206 (2014).

The rapid development of display technology in the early 21 st century has led to the widespread commercialization of different display products. One of the most popular display systems is the liquid crystal display ("LCD"). A common type of LCD is a twisted nematic liquid crystal display. It works by having two electrode surfaces that provide a uniform boundary condition, but two preferred orientation directions rotated 90 ° with respect to each other. In the absence of an electric field, a uniformly twisted nematic phase region across the thickness of the device is achieved. When an electric field is applied perpendicular to the thin liquid film, the dielectric anisotropy of the liquid crystal molecules causes them to be turned and aligned with the field direction. When the field is turned off, the molecules return to their original state.

Image contrast in an LCD device is achieved by using reflected light from optical polarizers near the surfaces of the two electrodes. The bottom LCD substrate is mirrored on the underside to achieve high reflectivity. Unpolarized light enters through the top of the device and is polarized parallel to the up-orientation direction. If the electrodes are in the "off" state, light travels through the device and the polarization follows the orientation of the liquid crystal molecules as they are twisted by 90 °. Next, the light passes through the bottom polarizer to the reflective surface, bounces off the bottom polarizer, reverses orientation again through the liquid crystal molecules and passes through unimpeded by the top polarizer. Thus, this "off state is bright for the viewer because they see the ambient light that enters the device first. For the "on" state, the light again enters the top polarizer, but now the electrodes are activated and the liquid crystal molecules are aligned perpendicular to the substrates. Thus, no rotation of the polarization direction occurs, and no light is reflected back to the viewer through the bottom polarizer. In this case, the "on" state appears dark to the observer. This "off" and "on" states produce acceptable image contrast for the display.

Three leading small form factor electronic display structures utilize reflective technology in one form or another; switchable mirrors moved to on/off positions (U.S. patent 5,083,857) and laser beam steering with scanning mirrors (U.S. patent 6,245,590) each require some type of light source to be integrated into their MEMS devices; liquid crystal on silicon ("LCoS") contains CMOS reflective layers (us 7,396,130 and us 2004/0125283) each requiring a polarized light source for the complete system; and active matrix OLEDs and LEDs; while less complex, it still benefits from additional polarizer elements to eliminate ghosting caused by reflection (us patents 5,952,789 and 9,159,700).

Many prior art display devices utilize additional polarizing elements to produce polarized light for use in the display. Unwanted objects that convert the electric field of light after emitting light from the active area of the device are common solutions. Examples of applications related to the present invention include, but are not limited to, external polarizing layers, independent polarization separation films with or without phase plates, periodic grating structures, and polarizing beam splitters (U.S. Pat. nos. 8,125,579, 6,960,010, 8,767,145, 7,781,962, 7,325,957, 7,854,514, and U.S. patent publication No. 2005/0088084).

In particular, U.S. patent publication No. 2008/0054283 uses a plurality of metal nanowires as polarization control layers that are structurally grown as additional semiconductor layers. One prior art example, WO 2012140257, utilizes a semiconductor chip that emits polarized light by incorporating a lattice structure to selectively enhance the desired radiation component to select which polarization state to emit. Nevertheless, this is still an additional element placed on the semiconductor chip for polarized light emission to occur, and the above-mentioned prior art does not mention how to actually incorporate polarization technology into a display product.

No prior art has been identified that describes a systematic approach to achieving selective polarization states for micro LED display purposes by utilizing various crystal planes of semiconductor materials.

A new type of emissive imager is disclosed in U.S. Pat. nos. 7,623,560, 7,767,479, 7,829,902, 8,049,231, 8,243,770, 8,098,265, 8,567,960, each of which is incorporated herein by reference in its entirety and is a micro-semiconductor emissive display device capable of efficiently producing the visible spectrum of electromagnetic radiation. Although the use of the disclosed emissive imager can be readily applied to general solid state lighting, display applications for such devices have been realized. The emissive "quantum photon imager" (QPI) emissive display device emits photons from the active region of a group III nitride semiconductor device and propagates the emitted light into free space. "QPI" is a registered trademark of Ostendo technologies, Inc. (assignee of the present invention). In addition to QPI imagers, in which each pixel emits light from a stack of solid state LEDs or laser emitters of different colors, imagers are also known which emit light from solid state LEDs or laser emitters of different colors arranged side by side with a plurality of solid state LEDs or laser emitters serving a single pixel. Such a device of the invention will be generally referred to as an emissive display device. Furthermore, the invention can also be used to create light sources for many types of spatial light modulators (SLM, microdisplay) such as DLP and LCOS, and furthermore can also be used as backlights for LCDs.

Drawings

In the following description, the same reference numerals are used for the same elements (even in different drawings). The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the exemplary embodiments. However, the present invention may be practiced without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. In order to understand the invention and to see how it may be carried out in practice, some embodiments thereof will now be described, by way of non-limiting example only, with reference to the accompanying drawings.

Fig. 1 depicts various crystal planes in a GaN crystal structure.

FIG. 2 illustrates a coordinate system for hexagonal crystals of GaN, where the z-axis is perpendicular tocPlane, y-axis perpendicular tomPlane and x-axis perpendicular toaA plane, and the relative positions of the three valence bands at the f point with respect to the m-plane, whereinE _v2 With the lowest energy (not ofE _v3 ）。

3A-3B illustrate views of a multi-color pixel including an emission surface of a prior art quantum photonic imager emission display device, shown from cPlane orIn a direction ofLight emission.

4A-4C illustrate views of a multi-color pixel comprising the emitting surface of a quantum photonic imager emitting display device of the present invention, showing light from a non-polar m-plane or as in FIG. 4CDirectional light emission.

Fig. 5A-5D illustrate various multi-colored pixel contact pads for a polarized light emitting quantum photon imager emitting display device of the invention, and cross-sections of a preferred embodiment of the invention showing X, Y and common contacts.

FIG. 6 illustrates a functional block diagram of a polarized light emissive quantum photonic imager emissive display device of the present invention.

Detailed Description

The QPI emissive display device described above is only one example of an emissive micro-scale pixel array and in the exemplary embodiments described below relates to U.S. patents 7,623,560, 7,767,479, 7,829,902, 8,049,231, 8,243,770, 8,098,265, 8,567,960. However, it should be understood that the illustrated QPI emitting display device is only an example of the types of light emitting devices that may be used in and manufactured by the present invention, some of which have been set forth above. Therefore, in the following description, references to QPI emissive display devices should be understood for specific purposes in the disclosed embodiments, and not as limiting in any way to the present invention, U.S. Pat. No. 7,623,560.

FIGS. 3A and 3B show the cross-section and light-emitting surface of a QPI emissive display device or QPI imager of the prior art ascPlanar, and FIGS. 4A-4C illustrate the preferred embodiment of the present inventionmA planar side view and a light emitting surface. The invention enables an emissive display device, such as a QPI emissive display device or QPI imager, to emit photons, either unpolarized light or linearly polarized light.

Figures 4A-4C illustrate by way of example, and not by way of limitation, a preferred embodiment of the present invention and illustrate a QPI emissive display device pixel structure comprising a stack of multiple solid state light emitting layers including a light emitting structure on top of a silicon based semiconductor complementary metal oxide (Si-CMOS) structure including circuitry for independently controlling the on-off state of each of the multiple solid state light emitting layers of the pixel structure. The surface dimensions of QPI emissive display device pixels are typically on the micro scale with pixel pitches ranging from 1 micron to 5 microns or more. The QPI emissive display device itself may comprise a one-or two-dimensional array of such pixels, achieving the user-desired pixel resolution in terms of the number of rows and columns forming the QPI emissive display device micro-pixel array.

The present invention addresses the need in the display art for a light source that can be customized to emit polarized visible light emissions in a variety of states. Light weight, small form factor, and low power consumption are key considerations recognized by manufacturers when designing display systems for the consumer market, particularly for human wearable devices. Items such as glasses, goggles, wristbands, watches, or medical device monitors (to name a few) may benefit from polarized light displays that are seamlessly integrated into products and do not disrupt end-user applications. To this end, the present invention allows for the integration of polarized light sources into QPI emissive display devices without the need for extraneous hardware that undesirably increases the display system or requires a higher power input for the same number of output photons.

In a preferred embodiment of the present invention, a multicolor electron emission display device is provided comprising a two-dimensional array of multicolor polarized light-emitting pixel structures, wherein each multicolor light-emitting pixel comprises a plurality of light-emitting structures made of a non-polar or semi-polar group III-nitride material system. The light emitting structures may each be configured to emit light of a different color and each stacked perpendicularly to a grid of vertical sidewalls that electrically and optically separate each multi-color pixel from adjacent multi-color pixels within the array of multi-color pixels. A plurality of vertical waveguides optically coupled to the light emitting structure to vertically emit polarized light generated by the light emitting structure from the first surface of the light emitting structure stack. The light emitting structure stack is stacked on the digital semiconductor structure on a second surface opposite to the first surface of the light emitting structure stack. A plurality of digital semiconductor circuits are provided in a digital semiconductor structure, each of which is electrically coupled to receive control signals from a periphery of the digital semiconductor structure or from a bottom of the digital semiconductor structure using plated through holes or plated interconnects on sides of the digital semiconductor structure (e.g., for connection to the outside world, as it were). A plurality of digital semiconductor circuits in the digital semiconductor structure are electrically coupled to the multicolor light emitting structures through vertical interconnects embedded within the vertical sidewalls to individually control the on/off state of each multicolor light emitting structure.

The prior art QPI emissive display devices are stand-alone emissive displays which do not require additional optical elements. A polychromatic photonic element layer, in this particular case GaN or other III-V or II-VI semiconductor material emitting unpolarized colored light, is incorporated into the device. The backbone of the pixel control logic is a digital semiconductor structure that has been bonded together to form a QPI emissive display device system. It may include digital drive logic circuitry that provides power and control signals to the stacked photonic semiconductor structure. The invention extends to other micro LED semiconductor arrays of QPI device structures described in U.S. Pat. nos. 7,623,560, 7,767,479, 7,829,902, 8,049,231, 8,243,770, 8,098,265, 8,567,960, or vice versa, by incorporating features that introduce intrinsic polarized light emission capabilities for various applications.

The photonic structure of a QPI emissive display device consists of one or more separate layers of semiconductor material. In the case of AlInGaN/GaN material systems for QPI emissive display devices, heteroepitaxial growth on sapphire substrates by growth techniques such as MBE, MOCVD or HVPEcAnd (4) a plane. Other substrate materials may be used, including but not limited to sapphire (Al) ₂O₃) Hexagonal polymorph of SiC, GaAs, Si, spinel (MgAl)₂O₄) Amorphous Silica (SiO)₂），LiGaO₂，LiAlO₂And ZnO. Recently, bulk (bulk) GaN substrates have shown promising results for photonic devices, but their higher price and accessibility remain an obstacle ((bulk))D. Ehrentraut, R.T. Pakalapati, D.S. Kamber, W.Jiang, D.W. Pocius, B.C. Downey, M.McLaurin and M.D' Evelyn, "High quality, low cost macromolecular bulk GaN substrates," Japan applied Physics, 52, 08JA01 (2013) and W.Jie-Jun, W.Kun, Y.Tong-Jun and Z.Guo-Yi, "GaN substrate and GaN homo-epixy LEDs: Progress and springs," Japan applied Physics, 24, 066105 (2015)) may however be combined into substrate materials. The substrate material selected is accompanied by a doped layer of AlN or GaN, followed by n-GaN: si, then a fixed number of InGaN/GaN Multiple Quantum Wells (MQWs) with various indium concentrations depending on the desired emission wavelength of the layer, then AlGaN electron barriers, and finally p-GaN: and Mg. The photonic structures are then patterned into an array of pixels and contacts are added for forming a QPI emissive display device. To implement the present invention, the growth direction of the photonic layers (e.g., GaN/InGaN) of QPI emissive display devices is considered as follows.

The orientation (particularly the atomic position and surface chemistry) of the substrate used to grow GaN affects the major crystal planes that will coalesce during epitaxial growth. Since the mid-70's of the 20 th century, studies were conducted to determine stable growth planes and preferred growth directions for various substrates and orientations of GaN material systems. Most of these studies have focused on sapphire, due to bulk Al₂O₃Crystals are readily available and have been used for semiconductor epitaxy (PA Larsen, "crystalline substrate in epitaxial beta silicon and sapphire," Acta Crystallographica, 20,599 (1966)). E.g. c-plane andaproducing smooth on planar sapphire substratescPlanar GaN and AlN (HM Manasenit, F.M. Erdmann and W.I. Simpson, "The use of metallic in The preparation of semiconductor materials: IV. The nitriles of aluminum and gallium", journal of The electrochemical society, 118,1864 (1971)). Ga-faces have been firmly determinedcPlanar wurtzite GaN is the preferred growth facet for planar thin film growth in this material system. However, with a material such as (100) LiAlO₂（P. Waltereit，O. Brandt，A. Trampert，H. T. Grahn，J. Menniger, M.Ramsteiner, M.Reiche and KH Ploog, "Nitride semiconductors from electronic fields for electronic white light-emitting diodes" Nature 406,865 (2000)), r plane Al ₂O₃(M.D. Craven, S.H. Lim, F.Wu, J.S. Speck, and S.P. DenBaars, "Structural characterization of Nonpolars (112 ̅ 0) a-plane GaN thin growth on (11 ̅ 02) r-plane sapphire" applied physical bulletin, 81,469 (2002), "6H-SiC (MD Craven, A. Chakraborty, B. Imer, F.Wu, S.Kerr, U.K. Mishra, J.S. Speck, S.P. DenBaars," Structural and electrical characterization of a-plane GaN growth a-plane SiC "physical Si. 0, 2132 (2003)), and more recently when implementedcLED growth structure with equivalent output power of plane counterpartmPlane andaplanar GaN-derived traction (m.c. Schmidt, k. — c. Kim, h. Sato, n. filrows, h. Masui, s. Nakamura, s.p. denbairs and j.s. Speck, "High power and High external efficiency m-plane InGaN light emitting diodes," japanese applied physics journal, 46, L126 (2007). examples of such non-polar and semi-polar films and applications are disclosed in, for example, U.S. patent nos. 8,728,938, 9,443,727, 8,629,065, 8,673,074, 9,023,673, 8,992,684, 9,306,116, 8,912,017, 9,416,464, 8,647,435, and U.S. patent publication nos. 2011/0188528 and 2014/0349427 (each of which are assigned to ostandown, each by applicant, and hereby incorporated by reference in its entirety.

The invention is beneficial to AlInGaN material systemcGrowth of semiconductor material is achieved on a planar oriented substrate to enhance the light output of a photonics layer, such as that found in QPI emissive display devices. The present invention solves the limitations of the random polarization state properties of prior art emissive display devices by utilizing non-substrate planar, polar or semi-polar GaN. To utilize this method in the fabrication of polarized emitting micro LED displays, such as QPI emitting display devices, a novel pixelation process is disclosed to account for the presence of chemical junctions due to different crystal orientationsThe surface-bound molecules are structured such that the polarized light source in the disclosed linear QPI emissive display device is a subversive technique over existing devices. The illustrated photonic layer(s) of the QPI emissive display device of the present invention are grown in a manner conducive to non-polar or semi-polar planar growth and formation into a final orientation. Substrates that can be used for growth in non-polar or semi-polar orientations include, but are not limited to, (100) LiAlO₂R plane Al₂O₃M plane Al₂O₃Hexagonal polymorphic forms of SiC, various spinels ((100), (110), MgAl₂O₄) Planar, with a (001) Si substrate, GaN bulk, with a hollow cut (miscut) (e.g., 7 deg.) mThe plane surface is provided with a plurality of parallel planes,aplanar or semi-polar. In addition, the laterally epitaxially overgrown faceted sidewalls of c-plane GaN may be used as non-planarcA planar oriented substrate. These various substrates will create non-c-plane orientations in the III-nitride material system and induce optical polarization anisotropy in the emitted light.

Another embodiment of the invention is in GaNcAn anisotropic strain is introduced in the plane. This also allows optical polarization to occur due to compressive or tensile strain on the GaN epitaxial layers.

Each layer within the stack of multiple solid state light emitting layers including the exemplary QPI emissive display device pixels (see fig. 4A-4C) is designed to emit different color wavelengths, allowing the QPI pixels to be controlled by their Si-CMOS to emit any desired combination of multiple colors; e.g., red (R), green (G), and blue (B), from the same pixel aperture to cover any desired color gamut with selected color coordinates based on the selected RGB emission wavelengths.

The manufacturing process of the preferred embodiment of the polarized light emission QPI emissive display device structure illustrated in figures 4A-4C comprises the steps described in the following paragraphs. The process begins with forming an array of QPI pixels on a topside surface of a semiconductor light emitting photonic wafer, epitaxially grown to grow from a non-polar m-plane or The light is emitted directionally. The process is thatReferred to herein as pixelation, involves etching the sidewalls of a pixel, approximately 1 micron in width and depth, using semiconductor lithography and etching processes to extend through the heterojunction diode structure of the semiconductor light emitting material. The etched pixel array sidewalls are passivated with a thin layer of silicon oxide or silicon nitride using a semiconductor deposition process, and then coated with a thin layer of reflective metal such as, for example, aluminum (Al). The pixel sidewalls are then filled with a metal, such as nickel, for example using a semiconductor metal deposition process. After processing the pixelated pattern on the topside surface of the polarized emitting photonic wafer, alignment marks are added on the wafer to help align the etched pixel pattern during subsequent processing.

The same topside surface pixelation process may be performed on multiple polarized emitting semiconductor light emitting photonic wafers, each having polarized light emission of a different wavelength, e.g., 465nm (b), 525nm (g), and 625nm (r)). The three top side surface treated polarized emitting semiconductor light emitting photonic wafers may then be bonded together in a stacked manner, as described in the following paragraphs, to form a polarized light emitting RGB QPI emitting display device.

After the topside surface of the polarization-emitting semiconductor light-emitting photonic wafer is pixelated, one of the topside contact metal patterns illustrated in fig. 5A-5C is deposited on each formed pixel array using a semiconductor metal deposition technique such as electron beam deposition. The contact metal pattern illustrated in fig. 5A may be used for blue (B) polarized light emitting photonic wafers and the contact metal pattern illustrated in fig. 5B may be used for the top sides of green (G) and red (R) polarized light emitting photonic wafers. The deposited contact metal is preferably a thin metal stack, such as Ti/Al, that forms ohmic contacts to the indium gallium nitride (InGaN) heterojunction diode semiconductor light emitting structure of the B, G, and R polarized emitting photonic wafers. The method comprises the following steps: blue (B) polarized light emitting Photonic wafer and contact Metal Pattern

After the contact layer is deposited, the top side of the B, G and R polarized light emitting photonic wafer is further processed to form pixel sidewalls through the semiconductor epitaxial layers, which includes etching the sidewalls of the pixels, passivation, then metallization and metal fill deposition. This step makes the sidewalls of the pixel conductive and optically blocking and reflecting. These features of the sidewalls of the pixels also prevent optical crosstalk between adjacent pixels, confine the generated light within the formed pixel reflective sidewall cavities, and serve as electrical interconnect vias to conduct electrical signals to the top-side contacts of the pixels and to the contacts of the pixels of the top-side stacked photonics layer.

In a preferred embodiment, to fabricate the polarized light emissive QPI emissive display device structure illustrated in figures 4A-4C, a glass wafer (not shown) may be used as the substrate on which the multi-layer pixel array structure is stacked, then bonded to the top side of a Si-CMOS wafer processed to include the same pixel contact pattern as the multi-layer pixel array structure stacked on the glass wafer.

In another preferred embodiment for fabricating a polarized light emissive QPI emissive display device structure, Si-CMOS is used as the substrate on which the multilayer pixel array structure is stacked, and then the pixelated multilayer wafer is bonded to a glass cover wafer. In either of the two embodiments described above, the processing steps are similar, and the former will be used as an example, not a limitation, to describe the remaining steps of a polarized light emission QPI display manufacturing process.

Figures 5A-5C illustrate three different metal contact patterns for the metal contact layer of a polarized light emissive QPI emissive display device micro-pixel deposited on the top side of the pixelated B, G and R photonic wafer using conventional semiconductor and photolithography and metal deposition. The pixel contact pattern shown in figure 5A can be used on the top side of a pixelated B photonic wafer to generate polarized light emissions of collimated (e.g., ± 17 °) to quasi-lambertian (e.g., ± 45 °) pixels when the diameter, height and spacing of the contact openings are selected to form a user-defined optical waveguide for extracting light emitted from a polarized light emission QPI pixel. The pixel contact pattern shown in figure 5B is used on the top side of the pixelated B photonic wafer to generate lambertian emissions from polarized light emission QPI pixels. The pixel contact pattern shown in figure 5B is also used on pixelated G and R photonic wafers to allow maximum light transmission from the lower to the upper layers of the structure of the polarized light emitting QPI pixel.

Yet another preferred embodiment of a polarized light emission QPI emissive display device pixel structure is illustrated in figure 4A, where a glass cover wafer is first processed to pattern an array of pixel-sized micro-optical elements or microlenses that match the polarized light emission QPI pixel array pattern. When a glass cover wafer with pixel-sized micro-optical microlens elements is used as the substrate on which the polarized light emission QPI multilayer stack is formed, the resulting pixel array has an increased ability to modulate the light emission direction of the pixels in addition to modulating pixel array color and brightness; the ability to modulate the light field for direct-view and wearable near-eye displays.

After the top side of the B-polarized light emitting photonic wafer is pixelated and its top side contact layer is deposited, the wafer is then bonded to a glass cover wafer using semiconductor bonding techniques (such as, for example, fusion bonding) with or without the incorporation of pixel-sized micro-optical microlens elements. The epitaxially grown sapphire wafer is then stripped using known semiconductor laser lift-off (LLO) techniques and the structure is thinned to remove the epitaxially grown GaN buffer, leaving a thin layer (< 2 microns) that includes the B semiconductor polarized light emitting heterojunction diode structure encapsulated within the sidewalls of the formed pixel. With the backside of the pixelated B-polarized light emitting photonic wafer exposed, the pixel array backside contact pattern illustrated in fig. 5B is deposited as a thin metal stack, such as Ti/Al, using semiconductor metal deposition techniques.

Here, the term "in-process QPI wafer" is used to refer to a processed multilayer stack wafer that incorporates multiple layers of the process stacked up to that point. When such terminology is used, the top side of the QPI wafer in processing thus (as illustrated) becomes the back side of the last layer bonded.

The top side of the QPI wafer in the process (which is the back side of the pixelated B-photolayer) is then processed to deposit a bonding interlayer containing electrical contact vias aligned with the array sidewalls of the pixels. The bonding interlayer is a thin layer of silicon oxide or silicon nitride deposited using conventional semiconductor deposition techniques such as, for example, Plasma Enhanced Chemical Vapor Deposition (PECVD). After deposition of the bonding interlayer, the in-process QPI wafer surface is planarized to a surface planarization level sufficient for bonding with the top side of the other wafer to form a multilayer stack of polarized light emission QPI emissive display device.

The top side of the QPI wafer in process (which would be the B-layer back side with the added bonding interlayer) is then processed to bond it to the G-photonic wafer top side. This is achieved using a semiconductor bonding process (such as, for example, fusion bonding) using aligned bonding of the pixelated G-photonic wafer with the top side of the wafer in QPI processing.

With the pixelated G-photonic wafer bonded to the in-process QPI wafer, the epitaxially grown sapphire wafer of the G-polarized light emitting photonic wafer is typically stripped using semiconductor laser lift-off (LLO) techniques, and the structure is thinned to remove the epitaxially grown GaN buffer, leaving only a thin layer (< 2 microns) that includes the G-semiconductor polarized light emitting heterojunction diode structure encapsulated within the formed pixel sidewalls. With the backside of the pixelated G-photonic wafer exposed, the pixel array backside contact pattern of fig. 5B is deposited with a thin metal stack, such as Ti/Al, using semiconductor metal deposition techniques.

The top side of the in-process NCP-QPI wafer (which is the back side of the pixelated G-photolayer) is then processed to deposit a bonding interlayer that contains electrical contact vias aligned with the array sidewalls of the pixels. The bonding interlayer is a thin layer of silicon oxide or silicon nitride deposited using conventional semiconductor deposition techniques such as, for example, Plasma Enhanced Chemical Vapor Deposition (PECVD). After deposition of the bonding interlayer, the in-process QPI wafer surface is planarized to a surface planarization level sufficient for bonding with the top side of the other wafer to form a multilayer stack of polarized light emission QPI devices.

The top side of the QPI wafer in process (which would be the G layer back side with the added bonding interlayer) is then processed to bond it to the R photonic wafer top side. This is accomplished using a semiconductor bonding process (such as, for example, fusion bonding) using an alignment bond of the pixelated R photonic wafer to the top side of the QPI in-process wafer.

The pixelated R-photonic wafer is bonded to an in-process QPI wafer, then the epitaxially grown sapphire wafer of the R-polarized light emitting photonic wafer is stripped, typically using semiconductor laser lift-off (LLO) techniques, and the structure is thinned to remove the epitaxially grown GaN buffer, leaving only a thin layer (< 2 microns) comprising the R-semiconductor polarized light emitting heterojunction diode structure encapsulated within the formed pixel sidewalls. With the backside of the pixelated R photonic wafer exposed, the pixel array backside contact pattern of fig. 5C is deposited with a thin metal stack, such as Ti/Al, using semiconductor metal deposition techniques.

As illustrated in fig. 5C, the top side of the wafer in QPI processing has three contact vias per pixel; a center contact via, which is a unique contact for the R-photonics layer of a pixel, an x sidewall contact via, which is a unique contact for the B-photonics layer of a pixel, and a y sidewall contact via, which is a unique contact for the G-photonics layer of a pixel. A common contact for the entire pixel array; that is, the three intermediate contact layers added on the top side of the B, G and R optical sub-layers are formed as common contact rails that extend to the peripheral edge of the polarized light emission QPI die where they are connected to a set of common contact vias, thereby forming a ring at the peripheral boundary of each polarized light emission QPI die comprising the in-process QPI wafer.

Then, the in-process QPI wafer top side includes an array of micro-scale contact vias, where the pixel center via is a unique contact of the R photo-layer of the pixel array, the x sidewall contact vias are unique contacts of the B excitation photo-layer of the pixel array, the y sidewall contact vias are unique contacts of the G emission photo-layer of the pixel array, and the ring of micro-vias at the peripheral boundary of each QPI die includes the in-process QPI wafer, thereby providing a common contact that includes all three photo-layers of the pixel array of the QPI multi-luminescent layer stack.

As illustrated in figure 5D, the top side of each QPI emissive display device die comprising a Si-CMOS wafer comprises an array of micro-vias having a pattern matching the pattern of the array of micro-vias of the in-process QPI wafer described in the previous paragraph. When the Si-CMOS wafer is aligned and bonded to the in-process QPI emission display device wafer using semiconductor bonding techniques (such as, for example, fusion bonding), the array of bonding interface micro-vias provides electrical contact between unique contacts of the array of multiple photonic layers of the pixel polarized polychromatic polarized light emission QPI emission display device and a common contact ring at the peripheral boundary of each die comprising the QPI emission display device wafer.

Of GaNcThe introduction of anisotropic strain in the plane allows optical polarization to occur due to compressive or tensile strain on the GaN epitaxial layers. In particular, if at least one of the layers is fabricated from a c-plane oriented GaN material system of epitaxial layers, wherein anisotropic strain is induced in the c-plane GaN, optical polarization in the emitted light from the light emitting structure occurs due to the presence of at least one GaN epitaxial layer (strain component)) Compressive or tensile strain). One way to achieve this effect is to intentionally introduce strain into the GaN layer. Growth of GaN on A-plane sapphire results in this strain and Al-rich AlN/Al_xGa_1-xN quantum well or Al_xGa_1-xAnd an N strain compensation layer. In this case, the Al-rich quantum well, the strain compensating layer would be an integral layer of the polarized light emissive structure. Nanostructures grown on the c-plane are another way to achieve polarized emission. Examples include photonic crystals, metal nanoparticles, elliptical nanorods, and nanograms. Also, in the case of elliptical nanorods and nanograms, the in-plane strain asymmetry is attributed to the generation of polarized light.

Figure 6 illustrates a functional block diagram of a multi-color polarized light emission QPI emissive display device. Figure 6 shows a multicoloured micro-pixel array of a QPI emissive display device driven by the control logic of the Si-COMS of the QPI emissive display device. Figure 6 also shows two possible embodiments of QPI Si-CMOS control logic with two possible interfaces. In a first embodiment ((a) above), the functions of the QPI Si-CMOS control logic include only multicolor, micro-pixel array drivers and QPI emissive display devices, in which case the control signals and pixel array bit fields, containing Pulse Width Modulation (PWM) bits for each color for each pixel from an external source, would be received. In a second embodiment ((B) above), the functionality of the QPI Si-CMOS control logic may additionally include the logic functionality required to generate PWM bit fields for a multi-color micro-pixel array.

In a second embodiment, QPI Si-CMOS control logic receives a serial bit stream containing an optically modulated video input and associated control data through its interface blocks. In this embodiment of a polarized multi-color emissive QPI emissive display device, the light modulated video bitstream received by the Si-CMOS control logic is processed by a color and brightness control block for degamma linearization, gamut transformation, white point adjustment and color and brightness uniformity correction across the micro-pixel array. The bit stream output of the color and brightness control block is then converted into a PWM bit field and then clocked into the pixel driver array incorporated within QPI Si-CMOS. Indeed, the latter embodiment of QPI Si-CMOS control logic for polarized light emitting QPI emissive display devices does not require external video streaming processing support and operates with a standard high speed interface such as a Low Voltage Differential Signaling (LVDS) interface. The latter embodiment of QPI Si-CMOS enables lower power consumption and smaller volume aspects for polarized light emission QPI applications. In any embodiment, the connection to the outside world may be, for example, as already described herein.

One of the main advantages of the described polarized light emissive QPI emissive display device is its low power consumption, which is achieved by a number of factors: (1) high Internal Quantum Efficiency (IQE) of its photonic layer; (2) high Quantum Yield (QY) conversion efficiency of direct polarized polychromatic light emission from its emitting multilayer; (3) increased optical aperture conversion efficiency of its VB excitation light by light confinement action of the NPC-QPI pixel optical cavity; (4) increased conversion efficiency of its VB excitation light by the light confinement action of the optical sub-cavity formed by the BPF layer and reflective sidewalls and contacts of the pixel; and; (5) the spectral shaping of the BPF layer of the pixel acts to match the HVS photopic response.

The low power consumption of the described polarized light emissive QPI emissive display device makes it very effective in display applications requiring higher brightness in terms of small volume and low power consumption, such as near-eye displays for virtual and augmented reality (AR/VR) applications. The wavelengths (only the primary colors listed) selected in the foregoing description of the various embodiments of the present disclosure are for exemplary purposes, and other selections of these wavelengths following the same method of the present invention are within the scope of the present invention. Furthermore, the emission of micro-scale pixels combined with the low power consumption of the described polarized light emission QPI emission display device makes it very effective in light field display applications that typically require higher brightness in terms of micro-scale pixel pitch, small volume and low power consumption, plus micro-pixels requiring directional modulation. Of course, a combination of these two display applications; that is, light-field near-eye AR/VR displays substantially benefit from the small volume, high brightness, light-field modulation, and low power consumption capabilities of the polarized-light-emitting QPI-emitting display devices of the present invention.

It should be noted that the emission wavelength values used in the foregoing description of the structure of the polarized QPI emissive display device of the present invention are exemplary illustrations of the method of the present invention. Those skilled in the art of light emitting structures will recognize how to use the disclosed methods of the present invention to create an emissive micro-pixel spatial light modulator with polarized light emission using different sets of light wavelengths to generate the different sets of emission wavelengths. Those skilled in the art will recognize how to produce a multicolor micro-pixel array device that emits polarized light using the disclosed method of optical confinement of polarized light emission QPI emissive display device structural pixels produced by reflective sidewalls, reflective contacts, and electrically interconnected sidewalls of the pixels having different design parameters.

It should also be noted that the non-polar and semi-polar crystal orientations of the polarized light emitting QPI emitting display device enable higher indium uptake in the epitaxial growth of InGaN/GaN heterojunction diode structures of semiconductor light emitting material. This higher indium uptake enables the emission of polarized long wavelength light in the amber (615 nm) to red (625 nm) range, with excellent IQE and saturation characteristics, and the fabrication of a highly efficient polarized light emissive QPI emissive display device with polychromatic emission covering the entire range of the visible spectrum. This is an important advantage of the polarized light emission QPI emissive display device described in the present disclosure, since it is a known challenge to achieve similar results using polar crystal orientation due to the segregation (segregation) of indium at high uptake rates.

It should also be noted that the methods described in this disclosure for fabricating emissive multi-color polarized light emission QPI display structures may be combined with the methods for fabricating non-polarized light emission QPI emissive display devices described in U.S. Pat. nos. 7,623,560, 7,767,479, 7,829,902, 8,049,231, 8,243,770, 8,098,265, 8,567,960, enabling the fabrication of multi-color emissive QPI emissive display devices having polarized and non-polarized light emission at different emission wavelengths across the visible spectrum. This light modulation capability enables new types of displays to benefit from both polarized and unpolarized light emissions emitted from an array of emissive micro-pixels at different emission wavelengths across the visible light spectrum.

It is also important to note that the method for manufacturing a polarized light emission QPI emission display device described in the present disclosure can be readily used to produce a polarized light emission QPI emission display device with single wavelength emission using only one photonic wafer with the desired emission wavelength by performing the described manufacturing process.

It will be readily understood by those skilled in the art that various modifications and changes may be applied to the embodiments of the present invention without departing from the scope of the present invention as defined in and by the appended claims. It should be understood that the foregoing examples of the invention are illustrative only and that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosed embodiments should not be considered limiting in any sense. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims (3)

1. A multicolor electron emission display device comprising a two-dimensional array of multicolor polarized light-emitting pixels, wherein each multicolor light-emitting pixel comprises:

A plurality of light emitting structures made of a non-polar or semi-polar group III nitride material system, each light emitting structure having an in-plane strain asymmetry due to compressive or tensile strain on at least one epitaxial layer for producing polarized light and each light emitting structure for emitting a different color, stacked perpendicularly to a grid of vertical sidewalls that electrically and optically separate each multicolor pixel from adjacent multicolor pixels within a multicolor pixel array;

a plurality of vertical waveguides optically coupled to the light emitting structure to vertically emit the polarized light generated by the light emitting structure from the first surface of the light emitting structure stack;

the light emitting structure stack is stacked onto a digital semiconductor structure through a second surface opposite to a first surface of the light emitting structure stack; and

a plurality of digital semiconductor circuits in the digital semiconductor structure, each digital semiconductor circuit electrically coupled to the multicolor light emitting structure through a vertical interconnect embedded within the vertical sidewalls to individually control an on/off state of each multicolor light emitting structure.

2. The multicolor electron emission display device of claim 1 wherein the digital semiconductor structures are electrically coupled to receive control signals containing Pulse Width Modulation (PWM) bits for each color of each pixel and a pixel array bit field from an external source to individually control the on/off state of each multicolor light emitting structure.

3. The multicolor electron-emitting display device of claim 1 wherein the digital semiconductor structures are electrically coupled to receive an optically modulated video bit stream, and further comprising the logic functions required to generate PWM bit fields for a multicolor micro-pixel array to control the on/off state of each multicolor light-emitting structure separately.