標準CMOS製程之單光子偵測器

Abstract

本論文主要為利用標準0.18 μm CMOS製程技術，設計出均勻內建電場以形成光偵測區域，並利用金屬光柵結構，來提升單光子偵測器之偵測效率。由於現今利用單光子偵測器的影像陣列在進行影像擷取時，係利用脈衝式藍光二極體，所以我們將偵測光波長設定在550 nm以下之藍光可見光波長範圍，藉以提升單光子偵測器在此偵測波段的偵測效率，在此我們利用Pwell形成guard-ring的方法，來避免元件的corner breakdown造成元件的提前崩潰。設計晶片面積約851×851μm2，崩潰電壓約為-9.9V。在直流響應的量測上，我們比較了不同面積及光柵結構下的響應率並且得到在藍光波段400nm、465nm分別因為光柵結構而提升1.04倍及1.53倍。暫態響應上，我們藉由400nm及780nm 脈衝雷射，得到預期中不同波長下吸收係數對元件操作速度之影響。最後我們藉由Passive quenching電路，將元件操作至崩潰電壓之上，設定RL在250kΩ，得到元件暗計數為1.3MHz(0.5V、25℃)，並且經由元件死亡時間(Dead time)校正入射光子數，量測出最高之單光子偵測效率為6%，單光子偵測效率因利用光柵結構提升約1.2倍，雜訊等效功率在1×〖10〗^(-13) WHz-1/2。

In this thesis, by using standard 0.18□m CMOS technology, we design a single-photon avalanche photodiode (SPAD) with uniform built-in electric field in light detection region. The metal grating structure is used to enhance the photon detection efficiency. Because the imaging system with SPAD array uses pulsed blue LED as lighting source, we aim at enhancement of detection efficiency below 550nm. We use P-well guard-ring to avoid the corner breakdown and, to enhance photon detection, the metal layers are used to implement grating structure in the active region. As a result, we can enhance detection efficiency and, at the same time, keep the response speed. We design 15 devices with a chip size of about 851×851 μm2 and the low breakdown voltage of -9.9V is obtained as expected. In DC response measurement, we compare responsivity between devices with different grating structures and, with one of the devices, a 50% enhancement of photo-responsivity measured with a 465nm blue-LED is achieved. The pulsed lasers of 400 nm and 780 nm are used to study the transient response of our SPADs and the results are consistent with the simulation. Finally, with a passive quenching method, we bias the SPADs above breakdown voltage with a load resistor (RL) of 250 kΩ. At an excess bias of 0.5 V, the dark count rate is about 1.3MHz at 25℃. By considering the dead time of SPADs, we get the effective incident photon numbers and obtain a peak photon detection efficiency (PDE) of about 6%. Most importantly, by using the metal grating, we improve the PDE by 20% and achieve a noise equivalent power of 1x10-13 WHz-1/2.