Introduction to SiPMs - Advansid（介绍SiPMsAdvansid）.pdf

Application Note Introduction to SiPMs Basic SiPM Structure and Operation The silicon photomultiplier is a radiation detector with extremely high sensitivity, high efficiency, and very low time jitter. It is based on reversed biased p/n diodes, it can directly detect light from near ultra violet to near infrared, and it is employed in all those applications where low light/radiation level must be measured and quantified with high precision. Light is made of photons (quantum of light). SiPMs are designed to have high gain and high detection efficiency so that even a single photon impinging on a SiPM pixel can be detected producing an output current pulse with a very low time jitter (100 ps). The structure of a SiPM allow “parallel” photon detection, meaning that more photons can be detected at the same time enabling photon counting. A SiPM consists of a matrix of small-sized sensitive elements called micro-cells (or pixels) all connected in parallel (Fig. 1 and 2). Each micro-cell is a Geiger-Mode avalanche photo-diode (GM-APD) working beyond the breakdown voltage (Vbd) and it integrates a resistor for passive quenching. The equivalent circuit of a GM-APD is shown in Fig. 3. Cd is the diode capacitance in reverse bias, Rs is the silicon substrate series resistance, and Rq is the quenching resistor (Rq Rs). There are three fundamental operation modes in a GM-APD: quiescent mode, discharge phase, recovery phase. In quiescent mode, the diode is reversed biased to Vbias = Vbd +Vov (Vov is the overvoltage, i.e., the excess bias beyond Vbd). The switch in the equivalent circuit of Fig. 3 is open and unless a photon is absorbed (or a dark event occurs), the diode remains in this condition with no current flowing (neglecting leakage currents). When a photon is absorbed (or a da