10 research outputs found
Analog SiPM in Planar CMOS Technology
Silicon Photomultipliers (SiPMs) are emerging single photon detectors used in many applications requiring large active area, photon number resolving capability and immunity to magnetic fields. We developed planar analog SiPMs in a reliable and cost-effective CMOS technology with a total photosensitive area of about 1Ă—1 mm2. Three devices with different active areas, and fill-factor (21%, 58.3%, 73.7%), have been characterized. The maximum photon detection efficiency is in the near-UV and tops at 38% (fill-factor included), with a dark count rate of 125 kcps. Gain and crosstalk depend on the active area size and are comparable to those of commercial best-in-class custom-technology SiPMs. However our full CMOS processing enables advanced SiPM single-chip systems where transistors and further on chip electronics can be integrated together with the detectors
Large area silicon photomultipliers allow extreme depth penetration in time-domain diffuse optics
We present the design of a novel single-photon timing module, based on a Silicon Photomultiplier (SiPM) featuring a collection area of 9 mm2. The module performs Single-Photon Timing Resolution of about 140 ps, thus being suitable for diffuse optics application. The small size of the instrument (5 cm Ă— 4 cm Ă— 10 cm) allows placing it directly in contact with the sample under investigation, maximizing that way the signal harvesting. Thanks to that, it is possible to increase the source detector distance up to 6 cm or more, therefore enhancing the penetration depth up to an impressive value of 4 cm and paving the way to the exploration of the deepest human body structures in a completely non-invasive approach
Fully CMOS analog and digital SiPMs
Silicon Photomultipliers (SiPMs) are emerging single photon detectors used in many applications requiring large active area, photon-number resolving capability and immunity to magnetic fields. We present three families of analog SiPM fabricated in a reliable and cost-effective fully standard planar CMOS technology with a total photosensitive area of 1×1 mm2. These three families have different active areas with fill-factors (21%, 58.3%, 73.7%) comparable to those of commercial SiPM, which are developed in vertical (current flow) custom technologies. The peak photon detection efficiency in the near-UV tops at 38% (fill-factor included) comparable to commercial custom-process ones and dark count rate density is just a little higher than the best-in-class commercial analog SiPMs. Thanks to the CMOS processing, these new SiPMs can be integrated together with active components and electronics both within the microcell and on-chip, in order to act at the microcell level or to perform global pre-processing. We also report CMOS digital SiPMs in the same standard CMOS technology, based on microcells with digitalized processing, all integrated on-chip. This CMOS digital SiPMs has four 32×1 cells (128 microcells), each consisting of SPAD, active quenching circuit with adjustable dead time, digital control (to switch off noisy SPADs and readout position of detected photons), and fast trigger output signal. The achieved 20% fill-factor is still very good. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
Fast silicon photomultiplier improves signal harvesting and reduces complexity in time-domain diffuse optics
We present a proof of concept prototype of a time-domain diffuse optics probe exploiting a fast Silicon PhotoMultiplier (SiPM), featuring a timing resolution better than 80 ps, a fast tail with just 90 ps decay time-constant and a wide active area of 1 mm2. The detector is hosted into the probe and used in direct contact with the sample under investigation, thus providing high harvesting efficiency by exploiting the whole SiPM numerical aperture and also reducing complexity by avoiding the use of cumbersome fiber bundles. Our tests also demonstrate high accuracy and linearity in retrieving the optical properties and suitable contrast and depth sensitivity for detecting localized inhomogeneities. In addition to a strong improvement in both instrumentation cost and size with respect to legacy solutions, the setup performances are comparable to those of state-of-the-art time-domain instrumentation, thus opening a new way to compact, low-cost and high-performance time-resolved devices for diffuse optical imaging and spectroscopy
SPICE Electrical Models and Simulations of Silicon Photomultipliers
We present and discuss a comprehensive electrical
model for Silicon Photomultipliers (SiPMs) based on a microcell
able to accurately simulate the avalanche current build-up and
the self-quenching of its Single-Photon Avalanche Diode (SPAD)
“pixel” with series-connected quenching resistor. The entire SiPM
is modeled either as an array of microcells, each one individually
triggered by independent incoming photons, or as two macrocells,
one with microcells all firing concurrently while the other one with
all quiescent microcells; the most suitable approach depends on
the light excitation conditions and on the dimension (i.e. number
of microcells) of the overall SiPM. We validated both models by
studying the behavior of SiPMs in different operating conditions,
in order to study the effect of photons pile-up, the deterministic
and statistical mismatches between microcells, the impact of
the number of firing microcells vs. the total one, and the role of
different microcell parameters on the overall SiPM performance.
The electrical models were developed in SPICE and can simulate
both custom-process and CMOS-compatible SiPMs, with either
vertical or horizontal current-flow. The proposed simulation tools
can benefit both SiPM users, e.g. for designing the best readout
electronics, and SiPM designers, for assessing the impact of each
parameter on the overall detection performance and electrical
behavior
Fast silicon photomultiplier improves signal harvesting and reduces complexity in time-domain diffuse optics
We present a proof of concept prototype of a time-domain
diffuse optics probe exploiting a fast Silicon PhotoMultiplier (SiPM),
featuring a timing resolution better than 80 ps, a fast tail with just 90 ps
decay time-constant and a wide active area of 1 mm2
. The detector is hosted
into the probe and used in direct contact with the sample under
investigation, thus providing high harvesting efficiency by exploiting the
whole SiPM numerical aperture and also reducing complexity by avoiding
the use of cumbersome fiber bundles. Our tests also demonstrate high
accuracy and linearity in retrieving the optical properties and suitable
contrast and depth sensitivity for detecting localized inhomogeneities. In
addition to a strong improvement in both instrumentation cost and size with
respect to legacy solutions, the setup performances are comparable to those
of state-of-the-art time-domain instrumentation, thus opening a new way to
compact, low-cost and high-performance time-resolved devices for diffuse
optical imaging and spectroscopy.Peer ReviewedPostprint (published version
Time-domain diffuse optical tomography using silicon photomultipliers: feasibility study
Silicon photomultipliers (SiPMs) have been very recently introduced as the most promising detectors in the field of diffuse optics, in particular due to the inherent low cost and large active area. We also demonstrate the suitability of SiPMs for time-domain diffuse optical tomography (DOT). The study is based on both simulations and experimental measurements. Results clearly show excellent performances in terms of spatial localization of an absorbing perturbation, thus opening the way to the use of SiPMs for DOT, with the possibility to conceive a new generation of low-cost and reliable multichannel tomographic systems
New frontiers in time-domain diffuse optics, a review
The recent developments in time-domain diffuse optics that rely on physical concepts (e.g., time-gating and null distance) and advanced photonic components (e.g., vertical cavity source-emitting laser as light sources, single photon avalanche diode, and silicon photomultipliers as detectors, fast-gating circuits, and time-to-digital converters for acquisition) are focused. This study shows how these tools could lead on one hand to compact and wearable time-domain devices for point-of-care diagnostics down to the consumer level and on the other hand to powerful systems with exceptional depth penetration and sensitivity
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CMOS Transducers and Programmable Interface Circuits for Resource-Efficient Sensing Applications
Modern sensors are complex systems comprising multiple sub-systems such as transducers, analog and mixed-signal interface circuits, digital processing circuits, and packaging. Over the last few decades, innovations in these sub-systems combined with their increased integration in complementary metal-oxide semiconductor (CMOS) processes have led to the rapid growth in sensors for the Internet-of-Things (IoT), wearable devices, and fundamental scientific instrumentation. This thesis introduces novel ideas for various parts of a sensor signal chain.
First, CMOS-based transducers (i.e. sensing elements) are introduced. Single-photon avalanche diodes (SPADs) fabricated in 0.18µm and 0.13µm standard CMOS processes are demonstrated and characterized for various optical sensing techniques. A resistor fabricated using standard CMOS-BEOL layers in a 0.18µm process is used to demonstrate a compact, fully-integrated single-element flow sensor occupying less than 0.065mm2.
Second, front-end interface circuits for single-photon optical detectors are introduced. A fully-integrated SPAD-based ambient light sensor using mostly digital circuits and fabricated in a 0.13µm CMOS process is highlighted. It consumes 125μW and achieves one of the lowest reported areas (0.046mm2) in the literature. A custom analog front-end (AFE) chip is fabricated in a 0.18µm CMOS process for interfacing with a commercial silicon photomultiplier (SiPM) for gamma spectroscopy. It incorporates tunability of dynamic range and integration time, thus making it suitable for different detectors (i.e. SiPM and scintillator crystal combinations).
Third, non-linear analog-to-digital converters (NL-ADCs) are explored as a viable alternative to linear ADCs for information-aware, non-uniform quantization and a widely reconfigurable piecewise-linear analog-to-digital converter (PWL-ADC) prototype chip (0.18µm CMOS) is used to validate this. With a 7-bit output word, it achieves 5.6-bit to 9.5-bit resolution in user-defined regions of the input full-scale range (FSR), while consuming 105µW at a sampling frequency of 42kHz. Measurements with recorded ECG waveforms are used to highlight the application-specific advantages of the PWL-ADC.
Finally, some of the aforementioned ideas are used at the system level in a gamma spectrometer realized on a printed circuit board (PCB). The PCB design includes the AFE and PWL-ADC IC chips, a commercial SiPM and scintillator crystal, and a FPGA-based digital back-end (DBE). Several linear and non-linear isotope spectra with variable energy bin-widths (dE/bin) are recorded and analyzed to demonstrate the utility of the proposed concepts for peak enhancement and improved peak discrimination in radiation spectroscopy