Single-photon Avalanche Diode Structure Research Articles

Reducing dark count of single-photon avalanche diode detector with polysilicon field plate

To suppress the effect of dark count noise on single photon avalanche diode (SPAD) detector, the mechanism and method of reducing the dark count rate (DCR) of SPAD device by using a polysilicon field plate is studied in this paper. Based on the 0.18-μm standard CMOS process, a polysilicon field plate located between the P+ active region and shallow trench isolation (STI) is deposited to reduce the dark count noise for a scaleable P+/P-well/deep N-well SPAD structure. Test results show that the DCR of SPAD device decreases by an order of magnitude after the deposition of polysilicon field plates, and its dark count performance at high temperature is even better than that of device without polysilicon field plate at room temperature. The TCAD simulation further indicates that the peak electric field in the guard ring region of the SPAD device is introduced into the STI by the field plate, and the overall electric field in the guard ring region is reduced by 25%. Finally, through modeling and calculating the DCR, the polysilicon field plate weakens the electric field of the guard ring region with high trap density, hence the trap-related DCR is significantly reduced. Therefore, the dark count performance of SPAD detector is effectively improved.

Note: Large active area solid state photon counter with 20 ps timing resolution and 60 fs detection delay stability.

We are reporting on the design, construction, and performance of a photon counting detector system, which is based on single photon avalanche diode detector technology. This photon counting device has been optimized for very high timing resolution and stability of its detection delay. The foreseen application of this detector is laser ranging of space objects, laser time transfer ground to space and fundamental metrology. The single photon avalanche diode structure, manufactured on silicon using K14 technology, is used as a sensor. The active area of the sensor is circular with 200 μm diameter. Its photon detection probability exceeds 40% in the wavelength range spanning from 500 to 800 nm. The sensor is operated in active quenching and gating mode. A new control circuit was optimized to maintain high timing resolution and detection delay stability. In connection to this circuit, timing resolution of the detector is reaching 20 ps FWHM. In addition, the temperature change of the detection delay is as low as 70 fs/K. As a result, the detection delay stability of the device is exceptional: expressed in the form of time deviation, detection delay stability of better than 60 fs has been achieved. Considering the large active area aperture of the detector, this is, to our knowledge, the best timing performance reported for a solid state photon counting detector so far.

Impact of silicide layer on single photon avalanche diodes in a 130 nm CMOS process

Single photon avalanche diode (SPAD) is an attractive solid-state optical detector that offers ultra-high photon sensitivity (down to the single photon level), high speed (sub-nanosecond dead time) and good timing performance (less than 100 ps). In this work, the impact of the silicide layer on SPAD’s characteristics, including the breakdown voltage, dark count rate (DCR), after-pulsing probability and photon detection efficiency (PDE) is investigated. For this purpose, two sets of SPAD structures in a standard 130 nm complementary metal oxide semiconductor (CMOS) process are designed, fabricated, measured and compared. A factor of 4.5 (minimum) in DCR reduction, and 5 in PDE improvements are observed when the silicide layer is removed from the SPAD structure. However, the after-pulsing probability of the SPAD without silicide layer is two times higher than its counterpart with silicide. The reasons for these changes will be discussed.

Cross-talk characterization of dense single-photon avalanche diode arrays in CMOS 150-nm technology

Cross-talk characterization results of high-fill-factor single-photon avalanche diode (SPAD) arrays in CMOS 150-nm technology are reported and discussed. Three different SPAD structures were designed with two different sizes (15.6 and 25.6 μm pitch) and three guard ring widths (0.6, 1.1, and 1.6 μm). Each SPAD was implemented in an array, composed of 25 (5×5) devices, which can be separately activated. Measurement results show that the average cross-talk probability is well below 1% for the shallow-junction SPAD structure with 15.6 μm pitch and 39.9% fill factor, and 1.45% for the structure with 25.6 μm pitch and 60.6% fill factor. An increase of cross-talk probability with the excess bias voltage is observed.

Evaluation of size influence on performance figures of a single photon avalanche diode fabricated in a 180 nm standard CMOS technology

We present the performance characteristics of a single photon avalanche diode (SPAD) fabricated in a 180 nm standard CMOS image sensor technology. The SPAD structure was implemented in 8 different diameters between 5 and 40 μm to determine the influence of size variation on the SPAD performances in terms of dark count rate, afterpulsing, efficiency and time resolution. The measurements show a dark count rate below 10 kHz at 15 °C with a low afterpulsing probability (0.2 % at an excess bias of 300 mV), a good Photodetection efficiency (~20 %) and a very good time resolution (<70 ps FWHM at 450 nm) .

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

We proposed the world's first flexible ultrathin-body single-photon 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.

Characterization of Single Photon Avalanche Diodes Fabricated by 0.13μm Flash Process Technology

Two different structures of single photon avalanche diode(SPAD) fabricated by 0.13 μm flash process technology are presented. The structure-1 uses low implanted p-well surrounding the active area as the guard ring which prevents the periphery breakdown, while for the structure-2, a virtual guard ring with the deep retrograde n-well doping is designed. The characteristics of the two detectors with the same active area diameter are presented. The two SPAD structures exhibit relatively different dark and light performance. The first structure exhibits a typical dark count rate of 18 kHz at the room temperature and a maximum photon detection efficiency of 15%, while the second structure exhibits a dark count rate of 23 kHz and a maximum photon detection efficiency of 28%. The comparison of the two structures is therefore promising for the further advanced SPAD design.

Note: Solid state photon counters with sub-picosecond timing stability

We are reporting on a design, construction, and performance of photon counting detector packages based on solid state sensors. These photon counting devices have been optimized for extremely high stability of their detection delay. The detectors have been designed for applications in fundamental metrology and optical time transfer. The single photon avalanche diode structure manufactured on silicon using the K14 technology is used as a sensor. The active area of the sensor is circular with a diameter of 100 or 200 μm. The sensor is operated in an active quenching and gating mode. The photon detection efficiency exceeds 40% in a wavelength range spanning from 500 to 800 nm. The timing resolution is better than 20 ps rms. Its detection delay is stable within ±600 fs over several days of operation, in a sense of time deviation the detection delay stability of 150 fs has been achieved. The temperature change of the detection delay is as low as 280 fs∕K. This timing performance is preserved even under extremely high background photon fluxes exceeding 100 Mc/s. The detectors have been qualified for operation in space missions.

Design Criteria for InGaAs/InP Single-Photon Avalanche Diode

We provide a detailed insight on the design of InGaAs/InP single-photon avalanche diode (SPAD) for 1.55- μm photon detection. In order to lower SPAD noise [the dark count rate (DCR)] without lowering photon detection efficiency (PDE) or increasing afterpulsing, it is important to optimize detector vertical layer structure and diffusion profiles. We present simulations of SPAD structures with different models, including custom ones. We discuss the influences of multiplication region thickness and doping, absorption region thickness, and electric-field distribution on SPAD performance. Multiplication region thickness strongly affects tunneling generation, whereas a thicker absorption region gives higher absorption efficiency but reduces trigger efficiency. Their optimal values depend on InP and InGaAs material quality and on device operating conditions. We show how electric field within InGaAs must be chosen as a tradeoff between heterobarrier transit efficiency and carrier generation.

A physically based model for evaluating the photon detection efficiency and the temporal response of SPAD detectors

After a brief review of the physics of photon detection in single photon avalanche diode (SPAD) devices, in this paper we will outline the principle of operation of a model we developed with the aim of calculating both photon detection efficiency (PDE) and temporal response (TR) of these detectors. Then we will apply the model to the devices currently available in order to critically analyze some experimental results. We will show in particular how the use of the model allows us to gain a better understanding of the influence of each device parameter in determining both the PDE and the TR. Finally we will discuss some modifications that can be applied to the device structure in order to overcome such limitations. Their effectiveness in improving both the PDE and the TR will be investigated by means of the aforementioned model. The aim is to provide the reader with an insight of which performances can be expected in the next few years if a strong development of the SPAD structure is pursued.