We report on the next generation of transmissive liquid crystal
micro-display technology based on single-crystal Si
backplane. The demand for ultra-high resolutions in combination with optimization of size, weight, and power are
driving Kopin AMLCD to resolutions as high as 2k x 2k. Several key developments are driving the aggressive
development of higher density, lower power AMLCD displays. We will review display performance improvements
resulting from a transition to 8" Si wafer processing, including smaller design rules and multi-level metal processing. In
addition, we will describe new technologies enabling ultra-low power consumption, wide operating temperature range,
and "Instant-On" display performance at temperatures as low as
-40° C. We will discuss how these technologies are
combined in advanced micro-displays, which are enabling the next generation of ruggedized imaging applications.
Hong Choi, Ollie Woodard, Bor-Yeu Tsaur, Brenda Dingle, Edward Yung, Jeffrey Greiman, Ngwe Cheong, Martin Metras, Wen-Foo Chern, Jason Lo, Pin Anupongongarch, Murshed Khandaker, Dave Costa, Frederick Herrmann, Hiap Ong, Colin Reese
We report the progress in full-color 0.97-inch-diagonal SXGA and 0.57"-inch-diagonal XGA active matrix
liquid crystal displays. The circuits for these displays are fabricated on 8-inch silicon-on-insulator (SOI) wafers,
which are then transferred to glass wafers to produce transmissive liquid crystal displays. Significant power
savings and display performance improvements have been made with innovations in display architectures and
the use of indium tin oxid (ITO) pixels. The new thin efficient backlight with improved color spectrum also
contributes to lower power consumption and better color gamut. The Mantech program for the SXGA display
has enabled the processing of many wafers to resolve various production issues, which will result in
substantially higher yield for the SXGA microdisplays.
Strained single-quantum-well GaInAsSb/AlGaAsSb diode lasers have exhibited room-temperature threshold current densities as low as 50 A/cm2, one of the lowest values reported for diode lasers at room temperature. These lasers, grown by molecular beam epitaxy, have emission wavelengths of approximately 2.05 micrometers, characteristic temperature of 65 K, internal quantum efficiency of 95%, and internal loss coefficient of 7 cm-1. Single-ended cw power of 1 W is obtained for a 100-micrometer-wide broad-stripe laser. Tapered lasers with a 140-micrometer aperture have exhibited diffraction-limited cw power up to 600 mW.
Laser efficiency is an important issue for mid-IR Sb-based semiconductor lasers. It has been the key limiting factor in the efforts to develop high power lasers in recent years. This paper reviews the basic aspects of the problem and discusses some recent results. A number of factors affect the efficiency, one of which common to many materials was a high internal loss that increases rapidly versus temperature. A major contribution to this internal loss is the large intervalence band carrier absorption that occurs in all mid- to-low-gap III-V semiconductors. Recent studies of both types of Sb-based laser materials with InAs-like valence band (InAsSb) and GaSb-like valence band (InAs/GaInSb/AlSb type-II quantum wells) have showed such a strong absorption. Coupled with the thermal effects, the internal loss behavior results in an efficiency roll-off that limits the power performance. Issues for the improvement of the efficiency are discussed.
GaInAsSb/AlGaAsSb multiple-quantum-well diode lasers grown by organometallic vapor phase epitaxy are reported. The laser structure consists of n- and p-doped Al0.59Ga0.41As0.05Sb0.95 cladding layer, Al0.28Ga0.72As0.02Sb0.98 confining layers, and four 15-nm- thick Ga0.87In0.13As0.12Sb0.88 quantum wells with 20-nm-thick Al0.28Ga0.72As0.02Sb0.98 barrier layers. These lasers, emitting at 2.1 micrometers , have exhibited pulsed threshold current densities as low as 1.2 kA/cm2.
The current status of InAsSb/InAlAsSb quantum-well (QW) lasers emitting between 3 and 4 micrometer is described. QW lasers grown on GaSb substrates, with emission wavelengths at approximately 3.9 micrometer, have operated pulsed up to 165 K. At 80 K, cw power of 30 mW/facet has been obtained. Ridge-waveguide lasers have operated cw up to 128 K. QW lasers grown on InAs have emission wavelengths between 3.2 and 3.55 micrometer. Broad- stripe lasers have operated pulsed up to 225 K and ridge-waveguide lasers have operated cw to 175 K. Theoretical analysis of the laser gain using a 6 by 6 k (DOT) p model to calculate the valence subband structure is reported.
The current status of GaInAsSb/AlGaAsSb quantum-well (QW) lasers emitting at approximately 2 micrometers and InAsSb/InAlAsSb QW lasers emitting at approximately 4 micrometers is described. At room temperature, GaInAsSb/AlGaAsSb lasers have exhibited pulsed threshold current density as low as 143 A/cm2 and cw power of 1.3 W from a 300- micrometers aperture. Ridge-waveguide lasers have operated cw up to 130 degree(s)C, with a maximum power of 100 mW in a single lobe at 20 degree(s)C. From a tapered laser, diffraction-limited cw power of 200 mW has been obtained. The InAsSb/InAlAsSb QW broad- stripe lasers have operated pulsed up to 165 K, with a characteristic temperature of 30 K up to 120 K. At 80 K, cw power up to 30 mW/facet has been obtained. Ridge-waveguide lasers have exhibited cw threshold current of 35 mA at 80 K, and operated cw up to 128 K.
Recent advances in GaSb-based crystal growth technology have led to the demonstration of high performance quantum well lasers which emit at mid-infrared wavelengths. In fabricating such lasers, techniques are utilized which are processing intensive and time consuming. In this work, we report on the use of a pulsed anodic oxidation (anodization) technique to fabricate low-ridge, wide-stripe GaInAsSb/AlGaAsSb lasers operating near 2 micrometers . The low-ridge stripe areas are defined in one, 5-minute processing step which converts the p+ layer outside the stripe area into a uniform, stable native oxide.
A number of double heterostructure and quantum well lasers with wavelengths approximately 3.1, 3.2, 3.4, 3.85 - 4.1, and 4.5 micrometers have been realized in InAsSb/GaSb and HgCdTe/CdZnTe material systems. Peak powers at the few W level and average power at the few hundred mW-level were obtained from optically pumped broad-area lasers at >= 80 K. Threshold, efficiency, internal loss, and gain saturation studies are reported. A compact laser package was built, using a high-power diode array for pumping and a Stirling pump for cooling. Its performance with a 4-micrometers laser is described.
The OMVPE growth and performance of graded-index separate-confinement heterostructure strained quantum-well InGaAs-AlGaAs diode lasers are reviewed. Broad-stripe lasers have exhibited Jth as low as 60 A cm-2 for a cavity length L equals 1500 micrometers and differential quantum efficiency (eta) d as high as 90% for L equals 300 micrometers . Similar heterostructures have been used to fabricate traveling wave amplifiers with a laterally tapered gain region that emit over 1 W cw in a nearly diffraction-limited spatial lobe at 0.98 micrometers , linear arrays of 200-micrometers -long uncoated ridge-waveguide lasers with average threshold currents of 4 mA and (eta) d approximately 90%, and high-power broad-stripe lasers with power conversion efficiency exceeding 50% at 75 degree(s)C.
Performance trends in the development of monolithic two-dimensional, coherent grating surface emitting (GSE) laser arrays are presented. Such GSE arrays now operate continuously to more than 3 W/surface and pulsed to more than 30 W/surface. They have obtained cw threshold current densities of under 140 A/cm2 with cw differential quantum efficiencies of 20 to 30% per surface. Linewidths in the 50 MHz range have been obtained with output powers of up to 270 mW per surface. The arrays typically consist of 10 to 30 mutually injection coupled gain sections with 10 laterally coupled ridge-guided lasers in each gain section. A single GaInAs strained-layer quantum well with a graded index separate confinement heterostructure geometry allows junction down mounting with light emission through the transparent GaAs substrate. A surface relief grating is used for feedback and outcoupling.
Two-dimensional surface-emitting AlGaAs diode laser array modules, each containing two 1 sq cm hybrid arrays, have been fabricated and tested. For quasi-CW operation, peak output powers greater than 300 W/sq cm appear to be easily achievable at repetition rates up to 500 Hz. The measurements also indicate that CW output powers of 100-150 W/sq cm can be achieved from these arrays.
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