Tieer Gu

25.1: Similarities between TFT Arrays for Direct‐Conversion X‐Ray Sensors and High‐Aperture AMLCDS

The fabrication and operation of a 14 in. × 8.5 in. TFT array for Direct Conversion X-ray sensors with 1536 by 2560 pixels is described. Similarities in process and design are discussed with TFT arrays for high aperture AMLCDS, that also use a low k inter-level dielectric to improve performance.

An amorphous silicon TFT with annular-shaped channel and reduced gate-source capacitance

An amorphous silicon thin-film transistor (a-Si TFT) with an annular-shaped channel is presented. The annular-channel TFT (AC-TFT) is fabricated using standard design rules with 4 /spl mu/m minimum feature size which is common in large area applications such as active matrix LCDs. The AC-TFT has two times smaller gate-to-source capacitance of about 50 fF in the on-state as compared to a conventional rectangular-channel TFT (RC-TFT) which has the same on-current of more than 10 /spl mu/A at V/sub gs/=20 V and V/sub ds/=10 V. Its off-current under illumination from the gate side is about ten times lower than that of the RC-TFT.

Thin-film transistor array technology for high-performance direct-conversion x-ray sensors

Thin Film Transistor (TFT) array technology is presented for Digital X-ray Sensors in Direct Radiography applications. Circuit simulations were performed to optimize the design of the TFT array. The sensor array uses a combination of a mushroom electrode with a high fill factor of 86% and a polymer passivation dielectric to minimize column capacitance and improve signal-to-noise ratio. A 14 in. X 8.5 in. sensor array with 1536 X 2560 pixels was developed using this technology. The TFT arrays are processed entirely in Class 1 clean room environments to eliminate line defects and minimize pixel defects. The best 14 in. X 8.5 in. panels have exhibited fewer than 0.001% pixel defects, as detected during in process testing prior to Se coating. In typical image quality comparisons with conventional X-ray film/screen combinations, the digital X-ray sensor exhibited equal or better performance than film-screens. Clinical studies were also conducted. Radiologists concluded that diagnostically significant projection radiographic images can be produced with the new digital X-ray sensor that are equivalent or superior to conventional film/screen images at the same X-ray exposures. The detector recently received FDA approval.