高能物理实验中低噪声顶层金属CMOS像素传感器设计

发布时间：2018-01-09 13:03

本文关键词：高能物理实验中低噪声顶层金属CMOS像素传感器设计　出处：《华中师范大学》2017年博士论文　论文类型：学位论文

【摘要】：随着核物理和粒子物理研究的不断推进,以无中微子双贝塔衰变0vββ和暗物质寻找为典型代表的低本底(低事件率、低电荷漂移速率)、低噪声实验逐渐成为高能物理领域未来的研究主流和热点。没有气体电荷雪崩增益且以气体或高压低温下的液体为媒介的时间投影室被视为低本底、低噪声实验研究的理想探测器。能够满足该应用需求且具有更高灵敏度的时间、空间及能量分辨率的低噪声、高密度、大阵列像素传感器是未来高能物理实验研究迫切需要的。本文主要研究工作是针对低本底、低噪声的电荷读出背景,研究开发出集直接电荷收集与信号处理于一体的像素传感器芯片,旨在解决无气体电荷雪崩增益的时间投影室中直接收集和测量电荷的问题。其具体研究内容和创新点体现在如下几个方面:1.提出了全新的直接电荷收集像素阵列的传感器结构:将芯片最顶层的金属层开窗成裸露的电极(Topmetal),并在其周围设计隔离的同层金属环(Guardring)结构。裸露电极用来直接收集电荷,金属环与裸露电极之间的电势差可形成聚焦电场,提高电荷收集效率。用这种传感器结构设计的Topmetal-Ⅱ-芯片进行了单个Alpha track的物理实验,结果表明:该芯片能够在室温空气环境下,直接观测到由241Am Alpha电离周围空气产生的单条电荷径迹。并且,在77 K液氮环境下也观测到芯片能直接收集电荷。2.解决了模拟读出过程中行列选择切换对电荷灵敏放大器(CSA)输出干扰的关键技术问题:模拟读出时行列选择切换会引入电荷注入导致CSA输出震荡,为此,在CSA与行列选择开关之间设计了一级源跟随电路,有效隔离了电荷注入干扰。通过优化单个像素版图寄生参数,减小了 CSA输入及反馈电容,增大了电荷转换增益,从而提高了模拟读出的信噪比。采用该技术的Topmetal-Ⅱ-芯片在室温空气环境和77 K液氮环境下的电学测试结果表明:模拟读出工作稳定,且等效电荷噪声(ENC)分别为13.9 e-和12.6 e-。3.提出了片内阈值补偿方法,提高了像素间阈值电压的一致性:在像素内部增设数模转换器(DAC),独立补偿每个像素的比较器阈值电压,减小了像素间因CSA输出噪声、比较器输出失调噪声以及工艺误差共同导致的阈值电压的离散度。Topmetal-Ⅱ-阈值扫描测试结果表明:采用该补偿后,像素阵列阈值电压基准电平的离散度减小了 7.5倍,即从35.9mV减小至4.8 mV。且在Topmetal-Ⅱ-的光学成像实验中,观察到了良好的成像效果,从而验证了数字读出通道设计的正确性。4.提出了通过可调截止频率滤波器降低CSA偏置电压噪声,从而进一步提高信噪比的方法。在Topmetal-Ⅱ-的基础上,采用此方法设计了多像素的Topmetal-Ⅱa和单点大像素的Topmetal-S芯片。Topmetal-Ⅱa和Topmetal-S在室温空气环境下的初步电学测试结果表明:Topmetal-Ⅱa模拟读出ENC相比于Topmetal-Ⅱ-减小了 1.5 e-,即从13.9 e-减小至12.4 e-;模拟读出的直流电平波动噪声减小了 22%,即从1.2 mV减小至0.936 mV;Topmetal-S模拟读出ENC为28.7e-,达到了预期的30e-以内。目前,Topmetal-Ⅱ-芯片已在兰州重离子加速器和伯克利88-inch回旋加速器上成功实现了无损伤、高位置分辨和高精度时间分辨的束流监控系统,它即将被应用于下一代癌症治疗和加速器储存环上的束流监控;噪声更低的Topmetal-Ⅱa芯片将会进一步提升该束流监控系统的性能;Topmetal-S单颗芯片的电学测试已近尾声,由127颗1 mm电极尺寸的Topmetal-S芯片拼成的“正六边形”大电极阵列正在研发中,它即将应用到Ovββ实验中。
[Abstract]:With the development of the nuclear physics and particle physics research progresses, the low background in neutrinoless double beta decay of 0V beta and dark matter for the typical (low event rate, low noise, low charge drift rate) has gradually become the field of high energy physics experiment for future research and the mainstream hot spots. No time projection chamber gas charge avalanche in order to gain and gas or high pressure low temperature liquid medium is regarded as a low background, an experimental study on low noise detector. It can meet the application requirements and has a higher sensitivity of the time, space and energy resolution, low noise, high density, high pixel sensor array is the future research of high energy physics experiments urgently need. This paper is mainly aimed at low background charge, low noise readout background, the research and development of a set of direct charge pixel sensor chip collection and signal processing in one, to Direct collection and measurement of charge time projection chamber to solve no gas charge avalanche gain in question. The specific research contents and innovations in the following aspects: 1. proposed a new sensor structure direct charge collection of pixel array chip: the top layer metal window into the bare electrode (Topmetal), the same layer a metal ring around the design and isolation (Guardring) structure. The exposed electrode used to directly collect charge, potential difference between the metal ring and the exposed electrode can be formed by the focusing field, improve the charge collection efficiency. Using this sensor structure design of single chip Topmetal- II - Alpha track physics experiment, the results show that the chip in air environment, directly observed by 241Am Alpha ionization ambient air produced by single charge track. And, in 77 K liquid nitrogen environment also observed chip Direct collection charge.2. solved in the process of selecting analog readout ranks of charge sensitive amplifier (CSA) output: the key technical problems of interference when selecting analog readout ranks will introduce the charge injection to CSA output shocks, therefore, in the CSA and switch between the ranks of a source follower circuit, effectively isolating the charge injection interference. Through the optimization of a single pixel layout parasitic parameters, reduce the CSA input and feedback capacitance, increases the charge conversion gain, thereby improving the analog readout signal-to-noise ratio. By using the technology of Topmetal- II - chip in air at room temperature and liquid nitrogen environment 77 K under the environment of the electrical test results show that the analog readout is stable and, the equivalent noise charge (ENC) proposed threshold compensation method of chip are respectively 13.9 e- and 12.6 e-.3., improve the consistency between pixels within the pixel threshold voltage: department number Analog converter (DAC), the comparator threshold voltage compensation of each pixel independently, reduces pixel for CSA output noise, dispersion of.Topmetal- II - threshold voltage of the comparator output offset noise and process error due to the threshold scan test results show that the compensated pixel array threshold voltage reference level dispersion decreases 7.5 times, the optical imaging experiments from 35.9mV reduced to 4.8 mV. and Topmetal- II - in the observed good imaging effect, which verifies the correctness of the.4. digital readout channel design is put forward through the adjustable cut-off frequency of CSA filter to reduce the noise of bias voltage, so as to further improve the signal-to-noise ratio. Based on Topmetal- - II, designed by the method of Topmetal- multi pixel II A and single pixel Topmetal-S chip.Topmetal- II A and Topmetal-S in air ring Preliminary test results show that the electrical environment: Topmetal- II a analog readout ENC compared to Topmetal- II - reduced by 1.5 e-, from 13.9 e- reduced to 12.4 e-; analog DC level readout noise fluctuation is reduced by 22%, which is reduced from 1.2 mV to 0.936 mV; Topmetal-S ENC analog readout 28.7e-, to achieve the desired the less than 30e-. At present, Topmetal- II - chip has been in Lanzhou heavy ion accelerator and cyclotron Berkeley 88-inch successfully realized no damage, high position resolution and high precision time resolved beam monitoring system, it will be applied to the next generation of cancer treatment and the accelerator storage ring beam monitoring; low noise Topmetal- II A chip will further enhance the beam performance of monitoring system; electrical testing of Topmetal-S single chip is nearing completion, by 127 1 mm hexagon electrode size Topmetal-S chip made " "The large electrode array is being developed, and it will be applied to the Ov beta beta experiment.

【学位授予单位】：华中师范大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TP212

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