总剂量效应对CMOS图像传感器中光电二极管钳位电压的影响

Influence of TID Effect on Pinning Voltage of CIS

摘要:

钳位电压(V_pin)是影响 CMOS 图像传感器(CIS)中钳位光电二极管(PPD)电荷转移效率和满阱电荷容量的关键物理量。在辐照条件下,V_pin受辐射总剂量(TID)增加而升高,因此研究其机理对抗辐照CIS的设计有重要意义。文章利用TCAD仿真软件分析了CIS器件的电学特性,研究了V_pin受TID影响的机理。结果表明,当辐照引起的氧化物陷阱电荷浓度达到3×10¹⁶cm-3时,浅沟槽隔离(STI)附近的耗尽区将PPD中的pin层与地极电学隔离,从而导致pin层电势易受到传输晶体管TG沟道电势影响而增加,使得相同电子注入条件下PPD可存储的电子增多,复位所需电压增大,导致V_pin随着辐射总剂量增加而增大。

Abstract:

Pinning voltage (V_pin) is the key parameter affecting the charge transfer efficiency and full well capacity of the pinned photodiode (PPD) in CMOS image sensor (CIS). Experimental results show that V_pin increases with the total radiation dose (TID) effect, so it is of great significance to study the reasons in the design of anti-irradiation CIS. In this paper, TCAD simulation software is employed to analyze the electrical characteristics of the CIS and study the mechanism of V_pin affected by TID. The results show that when the concentration of trapped charges caused by irradiation reaches 3×10¹⁶cm-3, the depletion region near the shallow trench isolation (STI) isolates the pin layer of the PPD from ground, which causes the potential of the pin layer to be easily affected by the transfer transistor channel to increase. Thus under the same electron injection, the number of electrons stored in the PPD increases and the reset voltage needs to be higher, and V_pin increases with the increases of TID.