Research On Structures And Characteristics For SOI Pixel Detector

Silicon-on-insulator(SOI)monolithic active pixel detectors have been developing fast in recent years.They have many attractive features such as no mechanical bump bonding,high speed,high density and small pixel size,low power consumption,small parasitic capacitances,low noise and large gain,high immunity to single event effect,no latch-up,and well 3D integration techniques.In SOI pixel detector,both semiconductor sensor and readout electronic are fabricated on the same wafer.The sensor can be fully depleted with best detection efficiency,and ASIC is based on standard CMOS process which enables complex design with high performance.So,SOI pixel detector is a very promising technologie due to these advantages.This paper mainly investigates three issues of SOI pixel detector: the effective shielding between the SOI circuits and sensor,including back-gate effect and sensor-circuit crosstalk;the charge collection and conversion gain;suppression of the total ionizing dose(TID)effect.The back-gate effect can be suppressed by reducing fully depleted voltage,or with backgate potential pinning.The sensor-circuit crosstalk is reduced with electrical shield.The key factors of charge collection and conversion gain are studied by analyzing various factors.The charge collection can be improved by adjusting the electric field in the depletion region and shielding the circuit and sensor.The capacitance of the charge collector is reduced with small well size,and then a high conversion gain can be realized.The radiation hardening by design is based on charge compensation.Through the relevant theoretical research and simulation data analysis,the results are summarized as follows:1.The study of the shielding between the sensor and the circuit of SOI pixel detectorThe models of back-gate effect and sensor-circuit crosstalk are given based on the structure of the SOI pixel detector.A SOI pixel detector with alternant n and p sensing volumes is proposed to suppress the back-gate effect.The fully depleted voltage can be decreased dramatically compared with the conventional SOI pixel detector.The potential under the buried oxide layer is decreased obviously and the back-gate effect is suppressed.Preliminary theoretical analysis and physical level simulations are also presented.In addition,another PAPT-SOI pixel detector,in which a multi-junction structure is introduced,is proposed to improve the effective shielding between the sensor and SOI circuits.The back-gate effect is suppressed with backgate potential pinning.The sensor-circuit crosstalk is reduced with electrical shield.The functions of charge collection and shielding are separated in PAPT-SOI.And the withstanding voltage provides enough room for choosing an appropriate biasing voltage under a fully depleted condition.2.The study of the charge collection and the conversion gain of SOI pixel detectorThe models of the charge collection and the conversion gain are given.A SOI pixel sensor with small detection p-well(SDW-SOI)is researched and simulated to reduce the sense-node capacitance while maintaining a widespread collection area and uniform field within the sensing volume.In this pixel structure,two p-doped wells are adopted.SDW-SOI collects charge with large p-well,but detects with small p-well.The conversion gain is increased and the increase is related to the size of the two p-doped wells.For another,the charge collection and the conversion gain of PAPT-SOI are also studied.The capacitance of the charge collector is reduced,and then a high charge-to-voltage conversion gain can be realized.The key factors of charge collection and conversion gain for PAPT-SOI are studied by analyzing various factors and comparing with other structures.3.The study of the TID effect and Radiation hardening of SOI pixel detectorThe principle and the model of the TID effect are given.According to the model,an advanced SOI pixel sensor with N-type anti-punch-through structure(NAPT-SOI)is proposed to suppress the effect of TID.The radiation hardening by design is based on charge compensation.BNW in NAPT-SOI is used as an electrode with controllable potential,which provides similar functionality as middle silicon in double SOI(DSOI).NAPT-SOI has better charge collection efficiency,and can implement the effective shielding between the SOI circuits and sensor by electrical shield with no need for the double SOI wafer.In addition,a simpler pixel structure(IAPT-SOI)based on NAPT-SOI is proposed to modify the BNW/BPW/NAPTI multi-well structure to BNW/BPW structure.A higher potential difference between BNW and BPW is realized.By a high voltage biased on BPW,IAPT-SOI can achieve a high withstanding voltage,a large lateral electric field and a well voltage range to satisfy the need of TID suppression.