不同偏置状态下4T-CMOS图像传感器的总剂量辐射效应

Total ionizing dose radiation effects in 4T-CMOS image sensors at different biased conditions

对不同偏置状态下的国产科学级0.18μm工艺掩埋型4T-CMOS有源像素图像传感器进行钴-60γ射线辐照和退火实验,研究总剂量效应对图像传感器的性能影响,并观察是否存在总剂量偏置效应。着重分析暗电流、满阱容量等参数随累积剂量的变化规律。实验结果表明随着辐照总剂量累加,暗电流前期缓慢增长,之后退化明显加剧,这主要是由于辐照致界面态和氧化物陷阱电荷密度增加。4T-CMOS图像传感器的暗电流主要由来源于STI界面,而辐照导致耗尽区展宽与STI接触使得暗电流增长加剧,同时,辐照导致的耗尽区展宽也引起满阱容量的下降。并且在4T-CMOS图像传感器的实验中没有发现明显的总剂量偏置效应。

To study the effect of total dose effect and biasing effect on image sensor performance,Cobalt-60 gamma ray irradiation and annealing experiments were carried out on 0.18μm process buried 4T-CMOS active pixel image sensor under different bias conditions.Emphasis was placed on the variation of parameters such as dark current and full well capacity with cumulative dose.The experimental results show that with the accumulation of total dose of irradiation,the dark current increases slowly in the early stage,and then the degradation is obviously aggravated.The main source of dark current in 4T-CMOS image sensor currents from STI interface and depletion width increase touching to STI,which aggravates degradation of dark current.Full well capacities have a drop after irradiation,which was due to the the photodiode capacitance decreases when the depletion width increases induced by radiation.And there is no remarkable biasing effect at 4T-CMOS image sensor.degradation of dark current.