Physics / mechanism
A Single-Photon Avalanche Diode (SPAD) is a reverse-biased p-n junction operated above breakdown voltage (Geiger mode). A single photon triggers a self-sustaining avalanche; quenching circuitry resets the diode in nanoseconds. Arrays integrate thousands to millions of SPADs (SiPMs in analog sum mode; dSiPMs with per-pixel TDCs for time-stamped data). Key parameters: photon detection efficiency (PDE, 50–60% peak in Si at 520 nm), dark count rate (DCR, <100 cps/μm² at RT for best-in-class), timing jitter (sub-100 ps FWHM), and fill factor (10–80%, boosted by microlenses). Leading processes: TSMC 40 nm BSI, STMicroelectronics 40 nm, Tower Jazz. Array sizes now reach 400×400 pixels with per-SPAD TDCs at 10 ps resolution.
Competitive landscape
Direct competitors: linear APD arrays (lower sensitivity, no photon counting), SiPM analog arrays (no spatial/timing resolution per pixel), EMCCD/sCMOS (higher pixel count but microsecond-scale timing). For LiDAR, dToF SPAD arrays compete with FMCW coherent LiDAR (no avalanche noise floor but requires narrow-linewidth laser + complex DSP) and iToF (Sony, TI; lower cost, worse range/ambient rejection).
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.