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从EQR15-HE~EQR15-LE,通过工艺和设计优化,器件特性取得一定改进:
(1)场致隧穿部分的DCR正比于器件内部电场强度,器件内部电场降低使得场致隧穿部分的DCR降低,因此,DCR随电场的斜率降低,即DCR随过偏压的斜率降低。
(2)电场强度的降低导致耗尽区宽度增大,使得SiPM微单元的等效电容减小,而增益正比于微单元等效电容及过偏压,因此与EQR15-HE相比,EQR15-LE增益随过偏压的斜率降低。两者温度系数的不同来源于耗尽区宽度的差异,耗尽区宽度越大温度系数越高[14],EQR15-LE具有更高的温度系数。每105个穿过高场区的载流子平均会产生3个串扰光子[15],这体现在对于单次雪崩事件而言,增益越高产生的串扰光子越多。因此,EQR15-HE与EQR15-LE增益及DCR随过偏压的变化趋势不同进而导致PDiCT的不同。
(3) PDE的大小由几何填充因子、量子效率、盖革效率决定。碰撞电离系数与电场呈指数关系且正相关[15],器件内部电场降低导致电子空穴的碰撞电离系数减小进而盖革效率降低,影响PDE,这体现在短波长处PDE的降低。与此同时,尽管盖革效率存在一定程度的降低,但PN结峰值电场降低使得耗尽区展宽,更深吸收长度的长波长光子量子效率反而提升,因此,长波长处PDE改变很小。
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表1为NDL EQR15-LE与滨松同类型S14160-3015 PS[5]的主要参数,两类器件具有相同的有效面积及微单元尺寸。两器件的动态范围近似一样,EQR SiPM的器件结构使得其几何填充因子更高,因而器件在各自的推荐偏压下(Vop),EQR SiPM有更优PDE。EQR SiPM与MPPC的增益相近,只是其DCR及PDiCT不及MPPC。EQR SiPM的结电容远小于MPPC,意味其输出信号脉宽更窄,在高计数率应用中,脉冲堆叠现象的影响会比MPPC小。
Research institute HAMAMATSU NDL Series S14160-3015 PS EQR15 11-3030 D Active area/mm2 3.0×3.0 3.0×3.0 Microcell size/μm 15 15 Microcell number 39984 40000 Breakdown voltage (Vb)/V 38±3 28±0.2 Recommended operating voltage (Vop)/V Vb+4 Vb+7 Photon detection efficiency (PDE) @Vop 32% @460 nm 46% @410 nm Gain @Vop 3.6×105 3.5×105 Dark count rate (DCR) @Vop Typical: 700 kHz Typical: 2 000 kHz Crosstalk probability @Vop <1% 11% Terminal capacitance/pF 530 48 Table 1. Main characteristic parameters comparison between NDL and HAMAMATSU SiPM
FBK于2018年报道出微单元尺寸为5 μm、微单元密度高达46190个/mm2的超高密度UHD SiPM[6],在接近6 V的工作条件下,增益约为1.8×105,在545 nm处,PDE约为12%,但DCR高于800 kHz/mm2。与其相比,EQR06 SiPM微单元密度低于UHD SiPM,在推荐过偏压处,增益为7×104,峰值波长处PDE为28%,DCR约为240 kHz/mm2,整体特性优于FBK 微单元尺寸为5 μm的UHD SiPM。
Recent research progress of silicon photomultiplier with epitaxial quenching resistor
doi: 10.3788/IRLA20210587
- Received Date: 2021-08-18
- Rev Recd Date: 2021-09-21
- Available Online: 2022-08-13
- Publish Date: 2022-08-05
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Key words:
- silicon photomultiplier /
- epitaxial quenching resistor /
- photon detection efficiency /
- dark count rate /
- dynamic range
Abstract: The Novel Device Laboratory (NDL) of Beijing Normal University has been developing a silicon photomultiplier with an epitaxial quenching resistor (EQR SiPM), which has a compact structure and a relatively simple fabrication process. Recently, to meet the requirements of nuclear medicine imaging, NDL has successfully developed an EQR SiPM with a microcell size of 15 μm and an active area of 9 mm2 by optimizing the device structure and fabrication technology. Compared to previous devices of the same type, the dark count rate (DCR) of the EQR SiPM is further reduced while still maintaining high photon detection efficiency (PDE). At an ambient temperature of 20 ℃ and an operating overvoltage of 7 V, the typical DCR is 226 kHz/mm2, and the peak PDE is 46%. In addition, to further increase the dynamic range of the EQR SiPM, NDL has developed an EQR SiPM with a microcell size of 6 μm, an active area of 9 mm2 and a microcell number of 244720. At an ambient temperature of 20 ℃ and an operating overvoltage of 7 V, the typical DCR is 240 kHz/mm2, and the peak PDE is 28%. It has large dynamic range that is very suitable for the measurement of high-energy cosmic rays and other applications in hadron calorimeters.