质子辐射下互补金属氧化物半导体有源像素传感器暗信号退化机理研究

对某国产0.5 μm工艺制造的互补金属氧化物半导体有源像素传感器进行了10 MeV质子辐射试验, 当辐射注量达到预定注量点时, 采用离线的测试方法, 定量测试了器件暗信号的变化情况. 试验结果表明, 随着辐射注量的增加暗信号迅速增大. 采用MULASSIS (multi-layered shielding simulation software)软件计算了电离损伤剂量和位移损伤剂量, 在与γ辐射试验数据对比的基础上, 结合器件结构和工艺参数, 建立了分离质子辐射引起的电离效应和位移效应理论模型, 深入分析了器件暗信号的退化机理. 研究结果表明, 对该国产器件而言, 电离效应导致的表面暗信号和位移效应导致的体暗信号对整个器件暗信号退化的贡献大致相当.

Dark signal degradation in proton-irradiated complementary metal oxide semiconductor active pixel sensor

In this paper, we discuss the dark signal increase in complementary metal oxide semiconductor (CMOS) active pixel sensor due to proton-induced damage, and present the basic mechanism that may cause failure. When the fluence of protons reaches a predetermined point, the change of dark signal of the device is measured offline. The experimental result shows that as the fluence of protons increases, mean dark signal increases rapidly. The main reason for dark signal degradation is: 1) the ionizing damage causes a build-up of oxide trapped charge and interface state at the Si-SiO₂ interface. The creation of the interface traps (with energy levels within the silicon bandgap), which can communicate with carriers in the silicon, gives rise to the thermal generation of the electron-hole pairs and, hence increasing the dark signals; 2) when protons pass through the sensor, there is a possibility of collisions with silicon lattice atoms in the bulk silicon. In these collisions, atoms can be displaced from their lattice sites and defects are formed. These resulting defects can give rise to states with energy levels within the forbidden bandgap. The increasing of dark signal is therefore one of the prominent consequences of bulk displacement. We use multi-layered shielding simulation software to calculate the ionization damage dose and displacement damage dose. Based on the comparison of the test data of gamma radiation, combined with the device structure and process parameters, a theoretical model for separation proton-induced ionization and displacement damage effects on CMOS active pixel is constructed, and the degradation mechanism of the mean dark signal is investigated. The result shows that the contribution of ionization effect induced surface dark signal and the contribution of displacement damage induced bulk dark signal to dark signal degradation of the whole device are roughly equal in this domestic CMOS active pixel.