APPLICATIONS OF TECHNOLOGY:
- Radionuclide medical imaging
- High-energy nuclear physics
- Radiation detectors for nuclear safeguards
- Molecular imaging equipment
- Optical communications
- Insensitivity to magnetic fields
- High photon detection efficiency (PDE)
- Good timing resolution
- Low power consumption
- Potentially lower cost
A Berkeley Lab team led by Woon-Seng Choong has come up with an innovative 3-D silicon photomultiplier (SiPM) design that performs the electronic readout functions on the back side of the detector, maximizing the microcell front side surface area for unimpeded photon detection. The result is a solid-state silicon device with high photon detection efficiency (PDE). The structure of the Berkeley Lab SiPMs also facilitates the coupling of the detection signals with an application-specific integrated circuit for signal processing and analysis. In short, the Berkeley Lab device at last brings solid state technology to advanced photon detection.
Using silicon wafers, the back side readout technology can be used to fabricate matrices of microcells operating in “Geiger mode,” capable of counting individual photons and resolving the energy required of medical and high-energy physics applications. Conducting columns of only 15–20 microns in diameter carry photon detection signals from the microcell surface to the bottom of the detector, where they can be processed with circuitries fabricated on the back side of the silicon wafer or directly coupled to an application-specific integrated circuit chip.
Unlike vacuum tube-based photon detectors, these highly efficient SiPMs can work inside powerful magnetic fields, a capability needed to achieve multi-modality imaging such as combined PET (Positron Emission Tomography) and MRI (Nuclear Magnetic Resonance Imaging). Because they can be fabricated using standard silicon processing technology, they potentially can be produced and operated at low cost. Larger devices can be fabricated from monolithic silicon or tiled together from individual SiPM’s.
The capability of these devices to work inside magnetic fields opens up new possibilities for highly sensitive photon detection not only in medicine, but instruments developed for high-energy physics. Highly efficient and compact solid-state photomultipliers will lead to improved gamma ray detectors that use scintillators to identify nuclear materials that might be smuggled in commercial cargo. The solid-state photomultipliers can also be used to produce more affordable instruments for molecular imaging relying on nanoscale light-emitting crystals, or in new generations of optical communications and computing equipment.
Photomultiplier tubes are essential components of sophisticated photon detection systems ranging from medical imaging scanners and cell sorters to high-energy particle counters and nuclear weapons detectors. Solid-state photon detectors are a compact and attractive alternative to these vacuum tube devices, offering features such as high gain, low bias voltage, insensitivity to magnetic fields, and good timing resolution. SiPMs developed in the past have had limited effectiveness because the photon illumination on these devices is partially blocked by supporting electronic circuitry on the front side surface. They have a relatively low “fill factor,” the fraction of detector surface area actually available for photon detection. The Berkeley Lab overcomes this limitation to offer the first viable solid-state alternative.
DEVELOPMENT STAGE: Proven principle.
STATUS: Patent pending. Available for licensing or collaborative research.
REFERENCE NUMBER: IB-3150