1
Pixelated CdZnTe detector based on Topmetal-IIa sensor Yan Fan 1 , Xiangming Sun 1 , Ping Yang 1 , Guangming Huang 1 , Zhen Wang 1 , Dong Wang 1 , Shuguang Zou 1 , Zili Li 1 , Ruiheng Sima 1 1 Department of Physics Science and Technology , Center China Normal University, Wuhan Hubei 430079, P.R.China Topmetal-II - is a direct-charge collecting pixel sensor with the Equivalent Noise Charge(ENC) of 13.9e- in the room air. A pixelated CdZnTe detector based on Topmetal-II - sensor works at a low bias voltage of -2V due to leakage current saturation. In order to improve the bias voltage of the crystal to achieve higher spatial resolution, as well as to keep the low noise, Topmetal-IIa has been designed. The new sensor has the same array scan module with Topmetal-II - , but three different sections of the charge-collection electrode named Topmetal and the same layer metal surrounding the electrode called Guardring. Section A has the opening exposed electrode and the Guardring covered by insulating layer, which is the same as Topmetal-II - . Section B has the both opening exposed electrode and Guardring. Section C has the opening exposed Guardring and the electrode covered by insulating layer. Preliminary experiments show that Topmetal-IIa sensor has low ENC similar to Topmetal-II - , and the pixelated CdZnTe detector could work with Topmetal-IIa sensor could work at a bias voltage up to several hundred volts as to achieve high spatial resolution. Topmetal sensor families are a series of novel direct- charge collecting pixel sensors. Topmetal-II - is representative sensor to collect charge, with the Equivalent Noise Charge(ENC) of 13.9e- at room temperature[1]. Besides, Topmetal-II - can also collect charge in the 77 K liquid nitrogen[2]. The charge-collection electrode of Topmetal-II - is the opening exposed most-top metal called Topmetal. And that the same layer metal called Guardring is manufactured surrounding Topmetal. A pixelated CdZnTe detector based on Topmetal-II - sensor works at a low bias voltage of -2V due to direct current saturation[3]. In order to improve the bias voltage of the crystal to achieve higher spatial resolution, as well as to keep the low noise, Topmetal-IIa has been designed. • Chip Size : 4mm*9mm • Three different Sections • Row : 45(15 rows each section) • Column : 216 • Pixel Number: 9720 • Pixel Size : 40μm*40μm • Top metal area: 24μm*24μm • Two output modes: Analog /Digital • Work in each mode or both modes • Analog mode ENC : <13e - Feature: E [1]. Mangmang An et al., A Low-Noise CMOS Pixel Direct Charge Sensor, Topmetal-II-, [J]. NIMA, Volume 810, 21 Feb, 2016, Pages 144-150. [arXiv: 1509.08611, 2015] [2]. Shuguang Zou et al., Test of Topmetal-II- in liquid nitrogen for cryogenic temperature TPCs, [J]. NIMA, Volume 830, 11 Sept, 2016, Pages 275-278. [3]. Shuguang Zou et al., A highly pixelated CdZnTe detector based on Topmetal-II- sensor[J], CPC, Volume41, 046003 (2017) 11th International “Hiroshima” Symposium on the Development and Application of Semiconductor Tracking Detectors ——HSTD11 in conjunction with 2 nd Workshop on SOI Pixel Detectors(SOIPIX2017) at OIST, Okinawa, Japan Abstract ID:134 Topmetal-II - Sensor Section A Section B Section C Photo of Topmetal-IIa Sensor Section A: The charge-collection electrode is the opening exposed most-top metal , the same layer metal called Guardring is manufactured surrounding topmetal. The Guardring is covered by an insulating layer. (The same structure as Topmetal-II - sensor). Section B: The charge-collection electrode is the opening exposed most-top metal , as well as the Guardring is opening exposed. Section C: The top metal is covered by an insulating layer, but the Guardring is openig exposed. The charge is collected by the top metal by Alternating Current (AC) coupling. Exposed top metal A passivation layer on top metal A passivation layer on Guardring Top metal Exposed Guardring 1. ENC Test (analog readout) (a) Baseline of one pixel output on the oscilloscope. (b) Response to Tail-pulse and the result of the trapezoidal filter. Injecting 10000 Tail-pulses with the amplitude of 20mV(Q in =20mV *2.04fF=254.6e - ) through Guardring to a single pixel. • ENC : 12.4e - 2. Alpha source Test in the air Topmetal-IIa sensor collected the charge directly(Section A and B) or indirectly(Section C) by the three different sections. Section A Section B Section C 2.5mm thickness High Voltage(HV) A pixelated CdZnTe detector based on Topmetal-II - sensor(the same structure as section A of Topmetal-IIa sensor) works at a low bias voltage of -2V due to direct current(DC) saturation[3]. • The charge will be collected by the top metal by AC coupling in section C, which will avoiding DC saturation. • The high voltage was set to the electrode on the top of the CdZnTe crystal, the output signal of the Topmetal-IIa sensor was demonstrated at the right-hand side. • At the bias voltage of -50V, the whole sensor work normally, but at the bias voltage of -100V, the output signal of Section A and Setction B are saturated, while Section C work well. • Section C of Topmetal-IIa sensor could collect charge indirectly without DC saturation. The output signal of Topmetal-IIa sensor with different bias voltage on CdZnTe • Topmetal-IIa sensor has low ENC(ENC <13e - ) similar to Topmetal-II - . • Topmetal-IIa has three different sections, and charges are collected directly by most-top metal in Section A and Section B, while charges are collected by top metal by AC coupling in Section C. • Section C pixels will be used in the pixelated CdZnTe detector at a bias voltage up to several hundred volts as to achieve high spatial resolution, without DC saturation. • Optimizing the parameters of Topmetal-IIa sensor to achieve the uniformity of the pixels. • The spatial resolution and the energy resolution of the pixelated CdZnTe detector with Topmetal-IIa sensor will be tested at a bias voltage up to several hundred volts .
