A significant breakthrough achieved in the production of high-performance SiPMs with epitaxial quenching resistors
Recently, a significant breakthrough has been achieved in the production of high-performance silicon photomultipliers (SiPMs) with epitaxial quenching resistors (EQRs).1 The EQR SiPM packaging production line, developed by CGN Capital Photonics Technology (Tianjin), has been successfully launched with a product yield exceeding 90%. This breakthrough has sparked new growth in China's semiconductor optoelectronic device industry.
The SiPM is a solid-state photon detector known for its high sensitivity and compact structure. It is a silicon chip that is composed of a series of miniature avalanche photodiodes (APDs), each operating in Geiger mode by being reverse biased above the breakdown voltage to realize the avalanche multiplication of photoelectrons. A special resistor is connected with each APD to quench the avalanche multiplication after detection. These micro APDs are operating independently, and their summed outputs are sensitive to injected light intensity, enabling single-photon detection and high gain comparable with traditional photomultiplier tubes (PMTs).
SiPMs are progressively replacing traditional PMTs across diverse fields, including high energy physics (where radiation hardness is a significant constraint), astrophysics, nuclear medical imaging, and autonomous driving, owing to their superior performance characteristics. In addition to their inherent advantages—excellent single-photon resolution, magnetic fields immunity, low operating voltage, compact size, and ease of integration—SiPMs are continually optimized for critical performance parameters such as enhanced photon detection efficiency (PDE), higher photon count rate, broader linear dynamic range, and cost-effectiveness to meet the increasing requirements in these fields and other advanced applications. Due to the compactness, good timing performance and insensitive to magnetic field, SiPMs are currently used for the most commercial clinical TOF-PET scanners, especially in the PET/MRI, PET/CT. Time-of-flight measurement in a PET system can improve the signal/noise ratio of the reconstructed images, reduce the radiation dose, and shorten the scan time. The latest EQR SiPMs (EQR20 series) demonstrate a short pulse width and a sharp rising edge, which could enhance its application in TOF-PET scanners. Besides, EQR SiPMs achieved a high fill factor (more than 40%) and a high microcell density (up to 2,500/mm2), which could achieve high energy resolution and broad dynamic range.
The quenching resistor is a critical component in SiPMs, enabling their operation in Geiger mode while ensuring stable and reproducible photon detection. Currently, polysilicon quenching resistors are widely used in commercially available SiPMs due to their tunable resistivity and compatibility with standard CMOS fabrication processes. However, the utilization of polysilicon resistors along with connected metal lines leads to the occupation of active area within the devices, diminishing the geometric fill factor and consequently decreasing the PDE, particularly in cases where there is a large number of pixels. To overcome the limitation of polysilicon resistors, an innovative paradigm integrating the quench resistor directly into the silicon bulk of the device was proposed by researchers in the Semiconductor Laboratory of the Max-Planck Society. Simulations and fabrication of prototype devices have also been performed to provide proof-of-principle results.
