Solid state imager including TFTS with variably doped contact layer system for reducing TFT leakage current and increasing mobility and method of making same

US5917199A · kind A · utility

Assignee

• OIS Optical Imaging Systems, Inc. · US

Inventors

• Young Hee Byun · Novi, US
• Yiwei Lu · Ann Arbor, US

Key dates

• Filing date: May 15, 1998
• Grant date: Jun 29, 1999
• Expiry date: May 15, 2018

Classification

• Technology area (CPC H): Electricity
• CPC primary: H10F39/191

Abstract

A TFT structure includes a variably doped contact layer system in order to reduce leakage current characteristics and increase mobility of the TFT. Such TFTs may be utilized in, for example, X-ray imagers or liquid crystal displays. In certain embodiments, the contact layer system is lightly doped adjacent a semiconductor or channel layer, and is more heavily doped adjacent the source/drain electrodes. The variation in doping density of the contact layer system may be performed in a step-like manner, gradually, continuously, or in any other suitable manner. In certain embodiments, the contact layer system may include a single layer which is deposited over an intrinsic semiconductor layer, with the amount of dopant gas being used during the deposition process being adjusted through the deposition of the single layer so as to cause the doping density to vary (increase or decrease) throughout the thickness of the system/layer.