Silicon photomultipliers (SiPM)



Silicon photomultipliers from Hamamatsu are called Multi-Pixel Photon Counters. These devices are solid state photodetectors that can be used for photon counting and other ultra-low-light applications. The MPPC is comprised of a high-density matrix of avalanche photodiodes which, when operated in Geiger mode, generates the high internal gain (~106) that enables single photon detection. MPPCs also offer high photon detection efficiency and excellent timing resolution, and have some unique advantages such as low bias voltage operation, ruggedness, resistance to excess light, and immunity to magnetic fields.


Applications: medical imaging, distance measurement (LIDAR), radiation monitoring, high energy physics, hygiene monitoring, fluorescence measurement, etc.




Key features of MPPC

  • High sensitivity (high gain, high photon detection efficiency)
  • Low noise (low dark current, low crosstalk, low afterpulsing)
  • Excellent photon counting capability
  • Excellent timing resolution
  • High resistance to mechanical shock & excess light
  • Immunity to magnetic fields
  • Low voltage operation & simple readout circuit
  • Room temperature operation
  • Various microcell sizes, active area sizes, and packaging
  • Available as multi-channel arrays
  • Available as modules (analog or digital output) or with a starter kit to expedite evaluation

Product catalog: MPPC for precision measurement
MPPC technical note (PDF file, 65 pages)

How it works

The basic element of a silicon photomultiplier (SiPM) is a tiny microcell, which is a series combination of an avalanche photodiode and a resistor. A single SiPM device can contain a few hundred to tens of thousands of microcells. These microcells are all connected in parallel, and so the SiPM is a two-prong device that produces a photocurrent (not image data). To operate a SiPM, the user typically applies a reverse bias voltage of 3 to 5 volts over the device's breakdown voltage. This puts the SiPM into Geiger mode. Photons striking a microcell while the SiPM is in Geiger mode will trigger an avalanche of charge carries inside the microcell, resulting in an output pulse. One microcell fires one pulse at a time, regardless of the number of incident photos. Two microcells firing at the same time will produce an output pulse with twice the amplitude.


MPPC technical note (PDF file, 65 pages)
A technical guide to silicon photomultipliers
See all SiPM technical articles

 

MPPC products

Single-element detectors



MPPCs for precision measurement deliver the high photon detection efficiency of previous MPPCs but with dramatically reduced noise factors (lower dark count, lower crosstalk, and lower afterpulsing). They also have a wider operating voltage range, which enables users to increase the applied voltage to get higher gain and higher photon detection efficiency.


See single-element MPPCs

Multi-element arrays



An array is a rectangular configuration of multiple units of MPPC for precision measurement. There is little dead space between each unit. An array's four-side buttable structure allows arrays to be tiled together to form even larger detectors. Arrays can be efficiently coupled to scintillators for applications such as PET. Customization is also possible.


See multi-channel arrays

 

Modules



Covering a wide range of light levels, MPPC modules are available in two types: digital output (for photon counting) and analog output. Modules contain a single-element MPPC, amplifier, temperature compensation circuit, power supply circuit, and other components needed to operate the detector. Modules for MPPC arrays are also available.


See MPPC modules

Accessories



To simplify the evaluation of various non-cooled MPPCs, Hamamatsu offers a starter kit that includes a sensor circuit board and a power supply circuit board. The MPPC power supply has a built-in temperature compensation function to stabilize operation of the MPPC in environments with fluctuating temperatures.


See accessories

 

Customization

The standard lineup of MPPC products hints at the many possibilities there are of customizing the MPPC to match specific needs. Hamamatsu can provide complete solutions to customers because of our vertical integration.


At the design stage, Hamamatsu offers expertise in detector design, optical simulation, scintillators, signal processing, ASIC design, packaging technologies, and more. We also have application-specific expertise from having developed our own time-of-flight PET modules, radiation detection modules, and Compton camera.


At the manufacturing stage, Hamamatsu has in-house control over every aspect of MPPC manufacturing from wafer processing to final device packaging, using many of our own technologies along the way — MEMS technologies for etching, nanoimprinting and 3D interconnects, and Stealth Dicing technology for high-quality die cutting. Each step is governed by stringent quality control.


Contact us for more information

 

How does MPPC compare to PMT?

Hamamatsu has the most comprehensive lineup of low-light detectors in the photonics industry, which enables us to make an unbiased evaluation of the different available technologies. In some cases MPPC will be the right choice, while in other circumstances a photomultiplier tube (PMT) will be the best fit. Let us help you review the requirements of your application to find the optimal detector for your needs.


Related content: SiPM vs. PMT for low-light detection (webinar recording, 60 minutes)


 

Application examples

Positron emission tomography (PET)


To facilitate the development of time-of-flight PET systems, Hamamatsu has developed MPPC modules specifically for this application. The modules consist of a multi-channel MPPC array, fast scintillator, low-power ASICs, and power supply. The modules deliver excellent time resolution (coincidence resolving time of 280 ps FWHM) to improve localization of the points of gamma emission. The modules can also be customized in a number of ways, for example by using MPPC arrays with a different number of channels or a different type of scintillator. Various other latter-stage circuit boards are also available.


The development of MPPC modules for TOF-PET derives partly from Hamamatsu's long involvement with PET technology, including the establishment of the Hamamatsu Photonics PET Center in 2003. Among recent innovations are a MPPC-based four-layer DOI (depth-of-interaction) detector that obtains high position resolution for the finding small lesions, and a fixation-free brain PET scanner that enables clear imaging of brain function while reducing patient discomfort.


Catalog: MPPC modules for PET
Technical information: MPPC modules for PET
Related content: High-resolution four-layer DOI detector
Related content: Fixation-free PET for brain imaging

 

 

Distance measurement (LIDAR)


For optical distance measurement, Hamamatsu has several types of photodetectors: MPPC, PIN photodiodes, avalanche photodiodes, hybrid devices that combine a photosensor with front-end IC to reduce external noise effects, and distance measuring image sensors. The appropriate choice of detector will depend on factors such as the typical distances the system is designed to measure, the environmental conditions in which the system will be deployed, and the system's optical measurement technique.


MPPCs are well suited for direct time-of-flight (TOF), a technique for long-range distance measurement that is being adopted by the automotive industry for LIDAR systems. TOF-based LIDAR systems use a highly directional light source to emit ultrafast light pulses ahead of the vehicle at a high repetition rate. Light that is reflected back to the system is then used to detect the movement of objects in the scene which are to be avoided by the moving vehicle. This reflected light will generally tend to be weakened by atmospheric conditions, and thus a high-sensitivity detector such as the MPPC is required.


New MPPCs for LIDAR have enhanced sensitivity at 905 nm (the wavelength commonly used for TOF LIDAR) and also high internal gain to keep their output signal above the noise floor of the system's electronics. The fast time response of the MPPC is also critical to making as many measurements of the scene as possible. Other features of the MPPC that recommend it for use in outdoor applications are low power consumption and its durability in a wide range of operating temperatures.


Specifications of new NIR-enhanced MPPC
Catalog: Photodetectors for LIDAR
Technical information: Detectors for distance measurement
See other sensors for Advanced Driver Assistance Systems (ADAS)

 

 

Radiation monitoring


Radiation monitoring is an application with implications for public health and public safety, and thus it is critical that the instrument's photodetector can reliably deliver accurate measurements. In this regard, the MPPC stands up to the test because: a) its high sensitivity enables detection of low levels of radiation; b) minimal variation in gain across its photosensitive area serves to reduce the uncertainty of measurement; and c) its excellent timing resolution provides the means to discriminate between neutrons and gamma rays, which is a step toward correct identification of a radionuclide.


As proof of the suitability of MPPC for radiation monitoring, Hamamatsu has developed a series of modules for detecting cesium-137. The modules contain MPPC, scintillator, signal processing circuit, temperature compensation circuit, A/D converter, and data interface. Most of the space inside the module is taken by the scintillator, as this leads to faster measurements — albeit at the cost of lower photon yield, which is why a high-sensitivity like the MPPC is required. But even so, the modules are very compact, allowing for easy installation in either portable radiation monitors or inline monitoring systems.


Hamamatsu also used MPPCs in a joint development project to build a small, lightweight, and low-cost Compton camera for use in field work to decontaminate radioactive materials. The Compton camera was used to capture high-precision images of radioactive hot spots within a scene in just a few minutes.


Datasheet: C12137 radiation modules
Press release: Compton camera

 

 

High energy physics


Silicon photomultipliers like the MPPC are well suited for detecting very weak scintillation light, and thus have been adopted for use in a growing number of high energy physics experiments. For example, the T2K experiment in Japan installed over 60,000 pieces of MPPC to monitor neutrino beams transmitted from a location approximately 300 km away from the detector.


More recently, Hamamatsu made improvements to a specialized MPPC for cryogenic physics experiments. The device ("VUV MPPC") is capable of detecting light down to 120 nm to cover scintillation wavelengths of liquid xenon and liquid argon, and comes with cryogenically compatible, ultralow RI packaging options. Dark matter research is one of the possible applications.


Related content: Poster presentation on VUV MPPC given at the International Conference on High Energy Physics (ICHEP), 2016

 

 

Hygiene monitoring


How is cleanliness monitored? The presence of adenosine triphosphate (ATP) on a surface can serve as a proxy indicator for microbiological contamination. You swab the surface, chemically treat the collected swab to dissolve cell walls, and put the swab in solution with luciferase and luciferin. If ATP molecules are present, then the luciferin will emit light. The intensity of this luminescence will be proportional to the amount of ATP in the sample.


Designers of portable instruments for hygiene monitoring will generally put sensitivity at the top of their list of photodetector requirements because the amount of detectable light can be limited in at least two ways. First, collecting light on a small detector is difficult as luciferin molecules are distributed throughout the sample volume and the excited luciferin emits light in arbitrary directions. Second, the cleaner the surface is, the lower the ATP content and thus the weaker the optical signal. Either way, the MPPC is well suited for the sensitivity requirement due to its very high built-in gain, which multiplies the amount of incident photons by 105 to 106 electrons per activated microcell at a time. In low-light applications, this gain produces a large electronic signal with which to exceed the noise floor of the instrument's readout electronics.


In addition to high sensitivity, there are other features of the MPPC that recommend it for use in portable measurement of bioluminescence assays. These include its low crosstalk (so as to suppress spurious signals which may result in false positives), low-voltage power requirements, compactness, and ruggedness.


See MPPC single-element detectors

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