Silicon nanocrystals have been prepared in thermally oxidized hydrogenated amorphous silicon (a-Si:H) and annealed silicon-rich oxynitride (SRON) films with [O/Si]=0.17 [N/Si]=0.07, in the temperature range 400-800°C and 850-1150°C respectively. Glancing Angle X-ray Diffraction (GAXRD) measurements show the presence of silicon nanocrystals embedded in silicon oxide films. Warren-Averbach Analysis of GAXRD data indicates the presence of ~9 nm silicon crystallites in a-Si:H films oxidized at 800°C. Room temperature photo-luminescence (PL) was observed from silicon nanocrystals embedded in oxidized a-Si:H films. Modeling the PL data indicates the presence of 6 nm silicon nanocrystals. This discrepancy is attributed to the columnar growth of silicon nanocrystals in thermally oxidized a-Si:H films. Silicon nanocrystals were not formed by thermal oxidation of SRON films under similar reaction conditions. However, silicon nanocrystals could be fabricated by annealing SRON films for 4 h in vacuum over the temperature range 850-1150°C. Silicon crystallite sizes remained constant (~4 nm) for films annealed below 1050°C and increased to 9 nm for films annealed at 1150°C. The presence of nitrogen played an important role in the silicon nanocrystal precipitation in SRON films. While the nanocrystal formation in a-Si:H films was due to oxidation and crystallization progressing simultaneously in the films, nanocrystal formation in SRON films appears to be due to the high temperature precipitation of excess silicon in the film.
Amorphous silicon photodiode technology is a very attractive option for image array integrated circuits because it enables large die-size reduction and higher light collection efficiency than c-Si arrays. The concept behind the technology is to place the photosensing element directly above the rest of the circuit, thus eliminating the need to make areal tradeoffs between photodiode and pixel circuit. We have developed an photodiode array technology that is fully compatible with a 0.35 um CMOS process to produce image sensors arrays with 10-bit dynamic range that are 30% smaller than comparable c-Si photodiode arrays. The work presented here will discuss performance issues and solutions to lend itself to cost-effective high-volume manufacturing. The various methods of interconnection of the diode to the array and their advantages will be presented. The effect of doped layer thickness and concentration on quantum efficiency, and the effect of a-Si:H defect concentration on diode performance will be discussed. The photodiode dark leakage current density is about 80 pA/cm2, and its absolute quantum efficiency peaks about 85% at 550 nm. These sensors have 50% higher sensitivity, and 2x lower dark current when compared to bulk silicon sensors of the same design. The cell utilizes a 3 FET design, but allows for 100% photodiode area due to the elevated nature of the design. The VGA (640 X 480), array demonstrated here uses common intrinsic and p-type contact layers, and makes reliable contact to those layers by use of a monolithic transparent conductor strap tied to vias in the interconnect.
Howard Abraham, Homer Antoniadis, Daniel Roitman, Kyle Frischknecht, Travis Blalock, Ken Nishimura, Thomas Knotts, Jeremy Theil, Chris Bright, Jeffrey Miller, Ronald Moon
Capable self-emissive polymers are being developed for use as emitting materials for a variety of display applications. This paper describes the use of standard CMOS integrated circuit silicon wafer technology along with a spin-cast polyfluorene-base polymer emissive layer, to demonstrate an XGA resolution, full video microdisplay. The silicon chip drive circuitry (Analog Pixel-APIX) is described along with results from our efforts to optimize the reflective anode, the semitransparent cathode process, and emissive cell construction. The 1024 X 768 pixel display achieves 200 Cd/m2 brightness at low power (<50 mW) with fast 1 usec response times. In addition, we summarize future directions to achieve color and the need to incorporate a production- worthy seal layer on microdisplays manufactured on silicon wafers.
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