Silicon photomultipliers, often called "SiPM" in the literature, are

solid-state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their ...

single-

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alwa ...

-sensitive devices based on

Single-photon avalanche diode A single-photon avalanche diode (SPAD) is a solid-state photodetector within the same family as photodiodes and avalanche photodiodes (APDs), while also being fundamentally linked with basic diode behaviours. As with photodiodes and APDs, a SP ...

(SPAD) implemented on common silicon substrate. The dimension of each single SPAD can vary from 10 to 100 micrometres, and their density can be up to 10000 per square millimeter. Every SPAD in SiPM operates in Geiger mode and is coupled with the others by a metal or

polysilicon Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry. Polysilicon is produce ...

quenching resistor. Although the device works in digital/switching mode, most of SiPM are an

analog device Analog devices are a combination of both analog machine and analog media that can together measure, record, reproduce, receive or broadcast continuous information, for example, the almost infinite number of grades of transparency, voltage, ...

because all the microcells are read in parallel, making it possible to generate signals within a dynamic range from a single

to 1000 photons for a device with just a square-millimeter area. More advanced readout schemes are utilized for the

lidar Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...

applications.A new generation, long distance ranging Time-of-Flight sensor based on ST’s FlightSense™ technology
/ref> The supply voltage (''V''_b) depends on APD technology used and typically varies between 20 V and 100 V, thus being from 15 to 75 times lower than the voltage required for a traditional photomultiplier tube's (PMT) operation. Typical specifications for a SiPM: * Photo detection efficiency (PDE) ranges from 20 to 50%, depending on device and wavelength, being similar to a traditional PMT * Gain (''G'') is also similar to a PMT, being about 10⁶ * ''G'' vs. ''V''_b dependence is linear and does not follow a

power law In statistics, a power law is a functional relationship between two quantities, where a relative change in one quantity results in a proportional relative change in the other quantity, independent of the initial size of those quantities: one q ...

like in the case of PMTs * Timing jitter is optimized to have a photon arrival time resolution of about 100-300 ps * Signal decay time is inversely proportional to square root of photoelectrons number within an excitation event * The signal parameters are practically independent of external magnetic fields, in contrast to vacuum PMTs * Afterpulsing probability (3-30%), defined as probability of spurious second pulses after single photon arrival * Dark count density is frequency of pulses in absence of illumination (10⁵-10⁶ pulses/s/mm²) * Small dimensions and lower voltages permit extremely compact, light and robust mechanical design SiPM for medical imaging are attractive candidates for the replacement of the conventional PMT in

PET A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence ...

and

SPECT Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is ...

imaging, since they provide high gain with low voltage and fast response, they are very compact and compatible with magnetic resonance setups. Nevertheless, there are still several challenges, for example, SiPM requires optimization for larger matrices, signal amplification and digitization.

Comparison to vacuum tube photomultipliers

Advantages

Compared to conventional PMTs, the photoelectron gain is typically more deterministic, resulting in low or even negligible

excess noise factor An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of ph ...

. As a result, the SNR (Signal/Noise Ratio) for a fixed number of detected photons can be higher than a PMT. Conversely, the stochastic gain of a PMT typically requires more detected photons to obtain the same SNR. Mass production of silicon electronics by multiple vendors allows SiPMs to be made very cheaply relative to vacuum tubes. Bias voltages are 10-100x times lower, simplifying electronics. In the red to near-infrared, silicon enables much higher quantum efficiency than available PMT photocathode materials. Dynamic range can be orders of magnitude larger than a PMT if large numbers of SPADs are arrayed together, enabling faster imaging rates or higher SNR without saturation.

Disadvantages

Dark current is typically much higher at a given temperature than a PMT. Thus, a SiPM may require subambient cooling while a PMT used in the same application may not, resulting in increased complexity and cost. Similarly, obtaining large active areas may be difficult due to higher dark counts per area than PMTs. The

impulse response In signal processing and control theory, the impulse response, or impulse response function (IRF), of a dynamic system is its output when presented with a brief input signal, called an impulse (). More generally, an impulse response is the reac ...

of a SiPM has a complex, multiexponential shape. Relative to a PMT, obtaining a symmetric pulse shape or uniform frequency response may require more complex analog filtering or pulse shaping electronics.

Comparison to avalanche photodiodes

Conventional

avalanche photodiodes An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of photo ...

(APDs) also produce an amplified analog current in response to light absorption. However, in an APD, the total gain is much lower and the

much higher. Conversely,

quantum efficiency The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a Magnetic Tunnel Junction. This article deals with the term as a measurement of ...

can be higher and

dark noise Darkness, the direct opposite of lightness, is defined as a lack of illumination, an absence of visible light, or a surface that absorbs light, such as black or brown. Human vision is unable to distinguish colors in conditions of very low ...

lower.

References

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Technology of Broadcom-SiPM

SensL Technical Note

Optoelectronics Silicon photonics devices Particle detectors Photomultipliers de:Photomultiplier#Alternativen

Comparison to vacuum tube photomultipliers

Advantages

Disadvantages

Comparison to avalanche photodiodes

See also

References