John R. Troxell

Polycrystalline silicon thin-film transistors on a novel 800°C glass substrate

A new polycrystalline silicon thin-film transistor (TFT) technology using a potentially low-cost glass substrate is reported. Transistors are made using modified conventional n-channel MOS processes at temperatures of 800°C or less, with a final hydrogen implantation step. These transistors show leakage currents of 2 × 10-11A/µm of channel width, ON-to-OFF current ratios of 1 × 104at Vds= 9.0 V, and good dc stability. This combination of polycrystalline silicon transistors on potentially low-cost glass substrates offers a new option in the choice of active device technology for large-area flat-panel liquid crystal displays (LCDs).

Laser-recrystallized silicon thin-film transistors on expansion-matched 800°C glass

Laser-recrystallized silicon thin-film transistors (TFTs) have been fabricated, for the first time, on a novel, potentially low-cost glass substrate, The 0.5-µm-thick silicon films were deposited along with appropiate dielectric layers on Corning Code 1729 glass substrates and recrystallized using an argon ion laser. The n-channel enhancement-mode transistors were made using conventional IC device fabrication procedures modified to have a maximum processing temperature of 800°C. Transistors made in the recrystallized silicon show field-effect electron mobilities as high as 270 cm2/V.s, approximately 15 times that of comparable devices made in as-deposited polycrystalline-silicon films. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do comparable polycrystalline-silicon devices.

Mosfet fabrication using ion beam nitridation

Ion beam nitridation has been suggested as an alternative to the conventional local oxidation process which is used in the fabrication of most metal-oxide-semiconductor (MOS) integrated circuits. The implantation of 2 keV nitrogen ions in doses of up to 8 x 1017 cm-2 results in the formation of a silicon nitride layer approximately 10 nm thick. Herein we describe the electrical characteristics of n-channel silicon gate metal-oxide-semiconductor-field-effect-transistors (MOSFETs) fabricated using this modified local oxidation process, and compare them to devices fabricated simultaneously but using the conventional local oxidation technology. The effective device channel lengths and widths are determined from the electrical characteristics of devices with mask (ideal) dimensions of 4, 6, 8 or 10 μm. The ion beam nitrided devices exhibit a significant reduction in the lateral oxidation effect. A 1.3 μm increase in channel width relative to conventional processing is observed for the ion beam nitrided devices with a 690 mm thick field oxide. On the other hand, fixed oxide charge densities are found to increase by a factor of about two due to the nitrogen implantation, and device channel mobilities are reduced by about 25%.

Reconfigurable head up displays for enhanced vehicle-to-driver communication

Head up displays offer the potential for improved vehicle to driver communication, particularly as new ITS features are implemented. In order to best address this opportunity, a fully reconfigurable high brightness active matrix vacuum fluorescent head up display has been developed. This display features a brightness of 9600 ftL, luminous efficiency of 14 lumens/W, and a small package size comparable to existing production fixed format vacuum fluorescent display systems.

Adhesion Effects on the Recrystallization of Silicon Films

Laser processing of thin films of amorphous or polycrystalline silicon on insulator substrates, such as the glass normally used for liquid crystal displays, frequently leads to film thickness variations which are unacceptable for device fabrication. Some thickness variations are caused by the high surface tension of molten silicon and the poor adhesion of the silicon to the substrate. Techniques to reduce this problem by increasing the adhesion of the film to silicon dioxide coated Corning 7059 glass substrates have been investigated. Two different approaches were used. First, silicon ions were implanted into the silicon-glass interface to increase the direct bonding of the silicon to the silicon dioxide. Second, layers of material known to exhibit better adhesion to both silicon and silicon dioxide were introduced between the silicon film and the glass substrate. Both techniques produced films which, after subsequent laser processing, showed significantly reduced thickness variations. These procedures make it possible to laser process thin films of silicon on Corning 7059 glass substrates under conditions which produce large grain polysilicon films without producing unacceptably large thickness variations or film cracking.

Materials and Processes For Silicon TFT's On Aluminosilicate Glass: An Alternative Soi Technology

As-deposited polycrystalline silicon and argon ion laser recrystallized silicon thin film transistors (TFTs) have been fabricated on Corning Code 1729 glass substrates. This novel aluminosilicate glass has an expansion coefficient matched to that of silicon and a chemical durability comparable to that of fused silica. N-channel enhancement mode transistors were made using conventional IC device fabrication procedures (including thermal oxidation to form the gate insulator) modified to have a maximum processing temperature of 800 C. The- polycrystalline silicon TFTs exhibit leakage currents of less than 2x10 -11 A/ μm; of channel width and good stability and reproducibility. Transistors made in the recrystallized silicon show field effect electron mobilities as high as 270 cm 2 /V s, approximately 15 times the mobility of comparable devices made in as-deposited polycrystalline silicon. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do the comparable polycrystalline silicon devices. Major advantages of this TFT technology include the use of a novel, potentially low cost glass substrate and the simultaneous processing of both polycrystalline and recrystallized silicon devices on the same substrate material. This approach represents a new avenue for the incorporation of active devices into a variety of applications including integrated active matrix displays.