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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...
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... To demonstrate the applicability of the scaling law analysis to practical situations, we performed a theoretical fitting with experimental results from the literature. Figure 10 shows experimental data from the literature [40] representing the pixel size dependence of the maximum PDP (shown as dots). Here, L a−a is assumed to be 8 µm. ...
... Figure 10. The measured PDP trend from the literature fitted by the theoretical equation [40]. The measured and fitted data are shown as dots and a dashed line, respectively. ...
... The extracted r in for the DCR could provide useful information to estimate the major source of the DCR. Figure 11. The measured DCR trend from the literature fitted by the theoretical equation [40]. The measured and fitted data are shown as dots and a dashed line, respectively. ...
The growing demands on compact and high-definition single-photon avalanche diode (SPAD) arrays have motivated researchers to explore pixel miniaturization techniques to achieve sub-10 m pixels. The scaling of the SPAD pixel size has an impact on key performance metrics, and it is, thereby, critical to conduct a systematic analysis of the underlying tradeoffs in miniaturized SPADs. On the basis of the general assumptions and constraints for layout geometry, we performed an analytical formulation of the scaling laws for the key metrics, such as the fill factor (FF), photon detection probability (PDP), dark count rate (DCR), correlated noise, and power consumption. Numerical calculations for various parameter sets indicated that some of the metrics, such as the DCR and power consumption, were improved by pixel miniaturization, whereas other metrics, such as the FF and PDP, were degraded. Comparison of the theoretically estimated scaling trends with previously published experimental results suggests that the scaling law analysis is in good agreement with practical SPAD devices. Our scaling law analysis could provide a useful tool to conduct a detailed performance comparison between various process, device, and layout configurations, which is essential for pushing the limit of SPAD pixel miniaturization toward sub-2 m-pitch SPADs.
... The reported curve is the average of two measurements and the error bars show the range of measurement. PDP is a function of doping levels, noise, excess bias and active area [33], therefore the obtained PDP is achieved thanks to the low noise of device, compared to other 180 nm HV SPADs which will have comparable doping levels, and a larger active area in lieu of the square shape. Fig. 6 shows a state-of-the-art comparison in terms of DCR against PDP peak [22,30,31,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51], with diamond symbols denoting works in 180 nm lithography nodes and circle symbols for all the other nodes. ...
... PDP is a function of doping levels, noise, excess bias and active area [33], therefore the obtained PDP is achieved thanks to the low noise of device, compared to other 180 nm HV SPADs which will have comparable doping levels, and a larger active area in lieu of the square shape. Fig. 6 shows a state-of-the-art comparison in terms of DCR against PDP peak [22,30,31,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51], with diamond symbols denoting works in 180 nm lithography nodes and circle symbols for all the other nodes. For each symbol the corresponding reference number is inside the symbol (where possible). ...
... It can be easily noted that our device, when operated at both 4 V and 5 V, achieves the highest PDP peak in the 180 nm node, whilst in the same node the DCR value of our SPAD classifies second and forth lowest respectively. Work in [33] reports similar DCR to the DCR value of our SPAD with a reduced PDP peak value. Our SPAD compared to the other works in the 180 nm node [35,42] shows a higher PDP peak at a lower DCR value. ...
We present the design and application of a 64x64 pixel SPAD array to portable colorimetric sensing, and fluorescence and x-ray imaging. The device was fabricated on an unmodified 180 nm CMOS process and is based on a square p+/n active junction SPAD geometry suitable for detecting green fluorescence emission. The stand-alone SPAD shows a photodetection probability greater than 60% at 5 V excess bias, with a dark count rate of less than 4 cps/µm2 and sub-ns timing jitter performance. It has a global shutter with an in-pixel 8-bit counter; four 5-bit decoders and two 64-to-1 multiplexer blocks allow the data to be read-out. The array of sensors was able to detect fluorescence from a fluorescein isothiocyanate (FITC) solution down to a concentration of 900 pM with a SNR of 9.8 dB. A colorimetric assay was performed on top of the sensor array with a limit of quantification of 3.1 µM. X-rays images, using energies ranging from 10 kVp to 100 kVp, of a lead grating mask were acquired without using a scintillation crystal.
... As shown in Fig. 1(a), a typical shallow P+/N-well junction structure is used to illustrate the modeling method of timing jitter. This SPAD device mainly consists of a P+ implantation layer and an N-well that form a shallow depletion region and two neutral regions [15]. Under the excess bias state, once the photons are incident onto these three regions, the photonic carriers will be produced and spread over the entire detection area, as shown in Fig. 1(b) and (c), respectively. ...
... [20]. Although the compared SPAD device is fabricated in a different 0.18 μm standard CMOS technology [15,20], it has the same P+/N-well structure (see Fig. 1(a)) and the same active diameter with our modeling device. Moreover, the two SPAD devices show almost the same breakdown voltage, indicating few differences in doping profiles between them, therefore there is good comparability between the measurement and computation results. ...
Timing jitter as a key performance of single-photon avalanche diode (SPAD) detectors plays a significant role in determining the fast temporal response behavior of the SPAD device. Nevertheless, few analytic models are developed to directly calculate the characteristic of timing jitter for its modeling difficulty. In this paper, we propose a simple analytic modeling method, which can predict the temporal response of SPADs, without using time-consuming Monte Carlo simulation. Model investigation incorporates avalanche current, avalanche buildup time and jitter tail under different conditions. Furthermore, the key model parameters provided by Geiger mode TCAD simulation allow an accurate prediction on timing jitter. Analytical results indicate that for a SPAD device structure with a shallow P+/N-well junction in a 0.18 μm CMOS technology, the Gaussian peak response with about 110 ps full-width at half-maximum (FWHM) and the exponential jitter tail are in good agreement with the measured data, validating the accuracy and feasibility of this modeling method.
... Nevertheless, these sensors show almost negligible after-pulsing (<0.2%), which is in line with other works [43] and can be avoided almost completely with a 200 ns of off time. The timing jitter for these sensors is expected to be below 80 ps for 1.4 V of overvoltage and 8 µm SPAD size, accordingly with similar SPADs [43]. are operated in gated mode to partially eliminate the after-pulsing and reduce the probability to detect dark counts instead of desired events [42]. ...
... The duration of INH at low level determines the off time, which should be held relatively large to avoid the afterpulsing. Nevertheless, these sensors show almost negligible after-pulsing (<0.2%), which is in line with other works [43] and can be avoided almost completely with a 200 ns of off time. The timing jitter for these sensors is expected to be below 80 ps for 1.4 V of overvoltage and 8 µm SPAD size, accordingly with similar SPADs [43]. ...
... Nevertheless, these sensors show almost negligible after-pulsing (<0.2%), which is in line with other works [43] and can be avoided almost completely with a 200 ns of off time. The timing jitter for these sensors is expected to be below 80 ps for 1.4 V of overvoltage and 8 µm SPAD size, accordingly with similar SPADs [43]. ...
We describe the integration of techniques and technologies to develop a Point-of-Care for molecular diagnosis PoC-MD, based on a fluorescence lifetime measurement. Our PoC-MD is a low-cost, simple, fast, and easy-to-use general-purpose platform, aimed at carrying out fast diagnostics test through label detection of a variety of biomarkers. It is based on a 1-D array of 10 ultra-sensitive Single-Photon Avalanche Diode (SPAD) detectors made in a 0.18 μm High-Voltage Complementary Metal Oxide Semiconductor (HV-CMOS) technology. A custom microfluidic polydimethylsiloxane cartridge to insert the sample is straightforwardly positioned on top of the SPAD array without any alignment procedure with the SPAD array. Moreover, the proximity between the sample and the gate-operated SPAD sensor makes unnecessary any lens or optical filters to detect the fluorescence for long lifetime fluorescent dyes, such as quantum dots. Additionally, the use of a low-cost laser diode as pulsed excitation source and a Field-Programmable Gate Array (FPGA) to implement the control and processing electronics, makes the device flexible and easy to adapt to the target label molecule by only changing the laser diode. Using this device, reliable and sensitive real-time proof-of-concept fluorescence lifetime measurement of quantum dot QdotTM 605 streptavidin conjugate is demonstrated.
... Consequently, from the moment that the photon is detected, all sel[i] signals are active for the rest of the measuring period. If, for example, the photon is detected in binpulse [1], like in The SPAD is implemented using a p+/n-tub junction on a psubstrate [34]. The active area of each sensor is octagonal with a 4 μm apothem. ...
Time-resolved fluorescence measurement is extraordinarily powerful in the analysis of substances due to its effectiveness in eliminating measurement artifacts. Some fluorescence measurements are still conducted on CMOS chips with the decay times determined after reading the data off the chip and fitting the fluorescence decay histogram. We present a novel approach in which an analog CMOS chip divides the fluorescence decay time into slices and classifies the photons according to their arrival times at a CMOS SPAD sensor. The chip was fabricated in a 1P6M 0.18 μm HV-CMOS process. The slice timings can be tailored from 168 ps to 4.9 ns, covering most fluorescence decay times. 9 timing windows are generated per pixel that count up to 13 b each, with a resolution of 0.16 mV/photon, for a maximum output voltage of 1.3 V, in an area of 150 μm x 50 μm. Here, we report on the first practical application of this circuit, which integrates an array of 5 pixels in a single chip and has an excitation light and a microfluidic circuit of up to 3 channels. This system could determine the decay time of quantum dots in 20 nl of solution. Thus, this work could help in the development of a Point-of-Care device based on time-resolved fluorescence.
... Moreover, a SPAD can operate in gating mode by biasing the junction above or under the breakdown voltage. The detail of the optical front end is depicted in Fig. 2. The SPAD is based on a P+/Nwell junction with a double Pwell/STI guardring [9]. The transistors MpQuench and MnQuench act as a passive quenching resistor and active quenching switch respectively. ...
CMOS single-photon avalanche diode (SPAD) array is a high-timing-resolution photon-counting image sensor. Pixel size shrinkage for high image resolution is highly desirable but hindered by the lowered photon-detection-probability (PDP) as the edge area becomes significant. We propose and demonstrate a parameter-free method for simulating PDP with the edge effect. Considering the doping profile, electric field, photon generation, and trigger probability distributions in two dimensions, the PDP reduction at the device edge is analyzed in a quantitative way. Besides, a novel guard-ring design for enhancing PDP of small SPAD has been proposed and simulated by our method. A threefold enhancement was obtained with the newly designed guard-ring structure compared with the original one. Our work is useful for developing small-pitch SPAD array for high-resolution imaging applications.
