Flexible ultrathin-body single-photon avalanche diode sensors and CMOS integration

Abstract

Abstract:We proposed the world's first flexible ultrathin-body singlephoton avalanche diode (SPAD) as photon counting device providing a suitable solution to advanced implantable bio-compatible chronic medical monitoring, diagnostics and other applications. In this paper, we investigate the Geiger-mode performance of this flexible ultrathin-body SPAD comprehensively and we extend this work to the first flexible SPAD image sensor with in-pixel and off-pixel electronics integrated in CMOS. Experimental results show that dark count rate (DCR) by band-to-band tunneling can be reduced by optimizing multiplication doping. DCR by trap-assisted avalanche, which is believed to be originated from the trench etching process, could be further reduced, resulting in a DCR density of tens to hundreds of Hertz per micrometer square at cryogenic temperature. The influence of the trench etching process onto DCR is also proved by comparison with planar ultrathin-body SPAD structures without trench. Photon detection probability (PDP) can be achieved by wider depletion and drift regions and by carefully optimizing body thickness. PDP in frontside-(FSI) and backside-illumination (BSI) are comparable, thus making this technology suitable for both modes of illumination. Afterpulsing and crosstalk are negligible at 2µs dead time, while it has been proved, for the first time, that a CMOS SPAD pixel of this kind could work in a cryogenic environment. By appropriate choice of substrate, this technology is amenable to implantation for biocompatible photon-counting applications and wherever bended imaging sensors are essential.

A Review on the Recent Progress of Silicon‐on‐Insulator‐Based Photodetectors

“…[33,34] The SOI APDs are designed to combine the advantages of this unique substrate with the quite high internal gain of the avalanche mechanism. [35,36] Compared with bulk silicon, the SOI technology enables perfect isolation between the APD and the readout circuit and thus achieves excellent noise performance. However, due to the ultrathin top silicon layer of fully depleted SOI, the light absorption is weak and hence decreases the quantum efficiency.…”

“…[ 33,34 ] The SOI APDs are designed to combine the advantages of this unique substrate with the quite high internal gain of the avalanche mechanism. [ 35,36 ]…”

Silicon single-photon avalanche diodes with nano-structured light trapping

“…The dark count rate (DCR) for both light trapping and control devices is around 40 MHz. This may come from epitaxy on SOI substrates, lack of a guard ring structure, and tunneling in the thin-junction 27 , 28 . To determine if nano-structures affect the DCR at a lower level, we reduced the DCR by two orders of magnitude through fabricating thicker-junction SPADs, both nano-structured and control devices, on a Si substrate, without the light trapping effect.…”

Toward implantable devices for angle-sensitive, lens-less, multifluorescent, single-photon lifetime imaging in the brain using Fabry–Perot and absorptive color filters

“…The top grating diffracts incident light into a Talbot diffraction pattern 21 , while the bottom analyzer grating selectively transmits or rejects the formed peak intensities, giving rise to angular modulation. In this case, distances between mask and detector are on the order of the wavelength, allowing lens-less imaging to be achieved with much thinner devices, opening up applications for flexible 22 , stackable 23 , or implantable imagers 24 . Amplitude-modulating gratings, which can be fabricated directly in the back-end metal of a conventional semiconductor fabrication process, produce this angular sensitivity but with significant optical loss.…”