以標準0.35 um SiGe BiCMOS技術來實現高光響應度光電晶體光偵測器之分析及設計

Analysis and Design of High Photoresponsivity Phototransistor Photodetector (PTPD) in Standard 0.35 μm SiGe BiCMOS Technology

賴宇紳(Yu-Sheng Lai)

指導教授 ： 徐永珍

國立清華大學/電機資訊學院/電子工程研究所/博士(2008年)

https://doi.org/10.6843/NTHU.2008.00688

摘要

The high performance phototranisitor photodetector (PTPD) has been realized in a standard 0.35 um SiGe BiCMOS technology without altering any process step. The surface photodetector (SPD) was introduced for enhancing light detection. The PTPD combines the conventional HBT with the extra detecting junction of SPD through the identical Base directly without external metallic interconnection. In our design, Emitter-Base (EB) junction just functions electrically, not for the light detection, and the SPD separated from Emitter plays an important role to absorb incident light, especially for short wavelength. The major part of the PTPD area can be left for the SPD to enhance light detection. Compared with the HPT of the same BC junction area, the shrunk Emitter area in PTPD reduces the device capacitance, as the SPD terminal is left floating. The unique structure of the PTPD allows one to obtain a high-sensitivity PTPD while simultaneously maintaining a small electrical capacitance. Therefore, the Emitter and the SPD areas can be respectively tailored for electrical and optical performance requirements.
The PTPD with floating Base and floating SPD, the normal operation configuration, benefits the requirements of low dark current, small device capacitance, light absorption, and ease of integrating PTPD with analog/digital circuits. In the normal operation, the maximum dark current of the PTPD with a Base-Collector (BC) area of 21 um x 25 um was measured to be 1.8 pA as VCE was swept from 0 to 1V. Measured responsivities of 5.2 A/W for 850 nm light and 9.5 A/W for a 670 nm light was obtained in this PTPD. At the same time, the strategies of spectral response design in PTPD are also provided in this thesis to mimic the spectral response of human eyes. For this purpose, the PTPD with Collector implantation was prepared and verified. It is worth mentioning that the process compatibility is still satisfied in this sample. The experimental results illustrated that the spectral peak of the implanted PTPD locates around the position of 500 nm wavelength.
For visible light applications, even when the incident light intensity is as weak as 0.01 lx, the PTPD can still generate significant photocurrent (0.25 nA at VCE = 1.5V, and 43 pA at VCE = 1.0 V). In addition, the operating voltage of PTPD can be as low as 0.3 V, which benefits portable device applications. The low cost, the high performance and flexibility in optical-electrical design make the PTPD suitable for the usage in many demanding applications.

關鍵字

光偵測器 ； 光電晶體 ； 光響應度 ； 矽鍺

並列摘要

本論文利用標準0.35 um SiGe BiCMOS製程技術在不更動任何製程步驟的條件下，實現ㄧ高效率的光電晶體光偵測器PTPD(Phototransistor Photodetector)的製作以及其特性分析。將表面光偵測器SPD(Surface Photodetector)與傳統的HBT(Hetrojunction Bipolar Transistor)經由共同的SiGe薄膜層直接整合形成PTPD。在元件的設計理念上，PTPD具有光電分離的優勢。雖然EB(Emitter-Base)接面與SPD接面是彼此分離並且位於相同深度(depth)，EB接面卻只負責電性行為，主要的光偵測區域是由SPD擔綱，所以EB接面的面積可縮小(需在輸出光電流可接受的前提下)換取將SPD的面積儘可能的擴大來改善光吸收效率。當SPD端電壓為浮接時，分析相同BC(Base-Collector)面積下的異質接面光電晶體HPT(Hetrojunction Phototransistor)與PTPD的寄生電容，可發現縮小的BE接面面積可降低元件的寄生電容。所以PTPD獨特的元件結構使得PTPD可同時兼顧高靈敏度與較小的元件寄生電容，所以EB接面面積與SPD的面積可個別設計來同時滿足電性或是光偵測等方面的種種特性要求。
當PTPD的基極(Base)與SPD是浮接時，PTPD具有低的暗電流(Dark Current)、較小的寄生電容、有效率的光吸收能力以及PTPD易於與周邊支援類比或數位電路直接整合。當PTPD的BC接面面積為21 um x 25 um而且VCE (Collector-Emitter 電壓)為0到1V時，實驗量得元件的暗電流最大值約為1.8 pA。光響應度(Photoresponsivity)在850 nm及670 nm量得的數據分別為5.2 A/W以及9.5 A/W。同時為了將元件應用於「類人眼」的場合，元件的光響應頻譜(Spectral Response)必須跟人眼類似，所以在不更動製程條件及步驟的條件下提出應用於PTPD的光響應頻譜調整方法-利用製程步驟中的集極佈植(Collector Implantation)來達成調整光響應頻譜的目標。實驗結果指出利用此種方法可將光響應頻譜的最靈敏波段調整至500 nm左右。
在可見光波段的應用上，當入射光低至0.01 lx時，PTPD仍然有明顯的光電流輸出(0.25 nA at VCE=1.5V，and 43 pA at VCE=1V)。除了PTPD對入射光強度具有高靈敏度外，PTPD的操作電壓可低至0.3 V，所以PTPD適合應用於手持移動式的產品。優秀的光電特性以及光電分離的設計理念使得PTPD可應用於許多方面。

並列關鍵字

photodetector ； phototransistor ； photoresponsivity ； SiGe

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