主動截止電路控制之單光子崩潰二極體偵測器

Abstract

本論文中，我們利用現今0.18 µm CMOS標準製程設計出一套主動截止電路﹙active quenching circuit, AQC﹚，以輔助先前設計的單光子崩潰二極體偵測元件﹙single-photon avalanche diode, SPAD﹚運作並增強其表現。傳統搭配被動截止電路的SPAD光偵測系統dead time太過冗長，因此AQC的首要設計目標便是縮短系統的dead time；而另一方面，AQC系統所佔面積太大將造成日後建構光偵測器矩陣時空間解析度低落，因此設計的另一目標便是縮減佔用面積。經過實際量測，我們設計的SPAD與AQC光偵測系統展現的dead time最短可達到4 ns，為參考文獻中最短紀錄；同時電路佔用面積15.7×15.2 〖µm〗^2亦為使用同製程文獻中最小者。除此之外，我們設計的AQC首創可調變hold-off time的功能，可依元件特性調整hold-off time長度，減低afterpulsing effect影響，換取較佳的dark counts表現，實驗中我們可讓dead time從4 ns延長至280 ns以上，並觀察到equivalent dark counts隨之降低。最後，我們透過不同的偏壓點驗證dark counts與偵測率﹙photon detection efficiency, PDE﹚隨著施加在SPAD上的超額偏壓升高而提升，實驗中PDE最高來到7.5%，同時雜訊等效功率﹙noise equivalent power, NEP﹚達到〖10〗^(-14) WHz^(-1/2)數量級。

In this work, we study single-photon-avalanche-diodes (SPADs) with an active quenching circuit (AQC) by using the standard 0.18 µm CMOS technology. Because the dead time of SPAD with passive quenching circuit is too long, the main target of the AQC design is to shorten it. On the other hand, the large chip area of AQC will reduce the spatial resolution of the fabricated SPAD array so to minimize the AQC is also important. Our SPADs with well-designed AQC show the fastest dead time of 4 ns, and use the smallest chip area of 15.7×15.2 〖µm〗^2, comparing with others using 0.18 µm CMOS technology. In addition, we demonstrate the function of tunable hold-off time which can be adjusted, according to the characteristics of SPAD, to reduce afterpulsing effect and to lower dark counts. The measured dead time can be extended to more than 280 ns, and the reduced equivalent dark counts are also obtained. Finally, we observe that dark counts and photon detection efficiency (PDE) both increase with increasing excess bias voltages. The highest PDE of 7.5% is achieved. The noise equivalent power (NEP) is about 10-14 WHz-1/2.