Boudry J M, Antonuk L E
Department of Radiation Oncology, University of Michigan, Ann Arbor 48109-0010, USA.
Med Phys. 1996 May;23(5):743-54. doi: 10.1118/1.597668.
The effect of 60Co radiation on the noise and drain-source current characteristics of hydrogenated amorphous silicon (alpha-Si:H) field-effect transistors (FETs) was examined as a function of dose to cumulative doses as high as approximately 2 x 10(4) Gy. Following these measurements, room-temperature and elevated-temperature annealing of induced radiation damage was examined. The FETs examined are representative of those incorporated in alpha-Si:H arrays under development for various x-ray medical imaging applications. No significant effect upon the noise characteristics of the FETs was observed as a result of the radiation. The predominant drain-source current effect with increasing dose was a shift of the transfer characteristic toward negative gate voltage and/or a decrease of the transfer characteristic subthreshold slope. This resulted in large increases in leakage current for gate voltages where the FETs were initially highly nonconducting. This leakage current increase was less pronounced for more negative gate voltages and was further diminished by maintaining the FETs at a more negative gate voltage during the irradiation. Following the radiation measurements, room-temperature annealing resulted in a 10% to 50% reduction in the leakage current in the first day followed by a logarithmic decrease thereafter. Elevated-temperature annealing for 2 h at 200 degrees C restored FET leakage current and threshold voltage properties to their preirradiation values. The irradiation effects are small for cumulative doses less than approximately 100 Gy, which is larger than the clinical lifetime dose for an imaging detector for chest radiography or for fluoroscopy (with infrequent exposure to the direct beam). For significantly higher dose applications such as mammography, fluoroscopy (with frequent direct beam exposure), and radiotherapy imaging, the results suggest that periodic elevated-temperature annealing or operation of the arrays at more negative gate voltages may be necessary.
研究了60Co辐射对氢化非晶硅（α-Si:H）场效应晶体管（FET）的噪声和漏源电流特性的影响，该影响是累积剂量高达约2×10⁴Gy的剂量函数。在这些测量之后，研究了诱导辐射损伤的室温及高温退火情况。所研究的FET代表了正在开发的用于各种X射线医学成像应用的α-Si:H阵列中所包含的FET。未观察到辐射对FET的噪声特性有显著影响。随着剂量增加，漏源电流的主要影响是转移特性向负栅极电压偏移和/或转移特性亚阈值斜率减小。这导致在FET最初高度不导电的栅极电压下漏电流大幅增加。对于更负的栅极电压，这种漏电流增加不太明显，并且通过在辐照期间将FET保持在更负的栅极电压下，漏电流进一步减小。在辐射测量之后，室温退火在第一天使漏电流降低10%至50%，此后呈对数下降。在200℃下进行2小时的高温退火可将FET的漏电流和阈值电压特性恢复到辐照前的值。对于累积剂量小于约100Gy的情况，辐射效应较小，该剂量大于胸部X线摄影或荧光透视成像探测器的临床使用寿命剂量（直接光束照射不频繁）。对于乳腺摄影、荧光透视（直接光束照射频繁）和放射治疗成像等更高剂量应用，结果表明可能需要定期进行高温退火或使阵列在更负的栅极电压下工作。
