Simulation of the Electrostatic Distribution in the Proximity Focusing Structure of an EBCMOS

Wei Wang,De Song,Ye Li,Weijun Chen,Xin Wang

doi:10.1109/jphot.2020.2989095

Wei Wang, De Song + Show 3 more

Open Access

https://doi.org/10.1109/jphot.2020.2989095

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Abstract

The electrostatic distribution of an electron bombarded CMOS (EBCMOS) was simulated by Ansoft Maxwell 3D software. Specifically, we studied how the electrostatic distribution was affected by the structure of a back-side bombarded CMOS (BSB-CMOS) and the anode position in electron-bombarded sensors. The simulation results reveal that the electrostatic field may cause a fault in the signal readout of the BSB-CMOS when the anode is positioned under the BSB-CMOS. In contrast, we found that the structure of an EBCMOS will aid electron focusing when the anode is positioned above the BSB-CMOS and the doping concentration of the electron multiplier layer is high. However, the high doping concentration of the electron multiplier layer will reduce the electron collection efficiency due to its rapid electron-hole recombination. We then designed a structure in which the multiplier layer has an overlying ultra-thin highly-doped layer, with an electrostatic distribution that functions to focus electrons. At the same time, this configuration can effectively prevent most of the multiplier electrons from recombining because ultra-thin highly-doped layer is much thinner than incident depth for the high-energy electron. This simulation study will provide a theoretical foundation for the fabrication of high-performance EBCMOS devices. Graphic abstract: a) EBCMOS physical model in Ansoft Maxwell 3D; b) The distribution of electrostatic distribution for BSB-CMOS with an ultra-thin heavily-doped layer. Electrostatic distribution of EBCMOS with different configurations were simulated. The results reveal that the electrostatic field may cause an erroneous readout of the BSB-CMOS if the anode is positioned under the BSB-CMOS. If the high voltage anode is positioned above the CMOS sensor, this is improved, especially when an ultrathin highly-doped multiplier layer is added to improve electron collection efficiency. This study provides a theoretical foundation for the fabrication of high performance EBCMOS devices.

Highlights

During the past two decades, digital readout techniques in low-light-level imaging devices have attracted much attention, as these devices can be widely used without the limitation of distanceVol 12, No 3, June 2020in applications such as criminal investigation, safety precautions, forest fire prevention and military reconnaissance [1]
The results reveal that the electrostatic field may cause an erroneous readout of the BSB-CMOS if the anode is positioned under the BSB-CMOS
1) The Influence of Doping Concentration on the Electrostatic Distribution When the Anode is Hollow: We assume that the inside of the anode in EBCMOS is hollow, and the structure is shown in Figs. 2 and 3(a) shows the electrostatic distribution in the EBCMOS when the doping concentration in the multiplier layer is assumed to be 1 × 1013 atoms /cm3

Summary

Introduction

During the past two decades, digital readout techniques in low-light-level imaging devices have attracted much attention, as these devices can be widely used without the limitation of distanceVol 12, No 3, June 2020in applications such as criminal investigation, safety precautions, forest fire prevention and military reconnaissance [1]. The electron-bombarded CCD/CMOSs have more advantages over low-light-level intensified camera systems including reduced sensor size and weight, increased sensitivity and dynamic range, faster response time, and better contrast and resolution. Compared to CCD cameras, each pixel of a CMOS cameras has its own amplification and read-out electronics, and can achieve faster frame rates than CCD cameras. CMOS sensor technology has developed at a rapid pace over the past two decades, replacing CCD cameras in consumer electronics and in scientific research. The development of EBCMOS cameras originated from applications in particle physics: Mimosa 5 was demonstrated in 2007, with 1024 × 1024 pixels, 40 Hz frame rate and an operating voltage of 6–10 kV [17]. The spatial resolution of EBCMOS is much lower than that of solid-state sensors, such as CMOS

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