Papers by Ryoichi Ishihara
Photon-counting imaging technology has applications in many fields such as fluorescence lifetime ... more Photon-counting imaging technology has applications in many fields such as fluorescence lifetime imaging microscopy (FLIM), time-resolved Raman spectroscopy, 3D imaging, and even space communications. The requirement to detect single photons with picosecond temporal resolution makes single-photon avalanche photodiode (SPAD) a popular choice. Advanced biomedical imaging applications such as pill cameras, retinal prosthesis, and implantable biocompatible monitoring sensors require a compact image system, which can be implanted into a living body. To meet these requirements, novel single-photon image sensor solution needs to be developed, in which new substrate post-processing and backside illumination or even dual-side illumination are core technologies, with inherent CMOS compatibility as a prerequisite. This chapter proposed and demonstrated the world’s first flexible CMOS single-photon avalanche diode image sensor, providing a suitable solution for implantable biomedical imaging or monitoring applications, and wherever a curved imaging plane is essential.
We present the first flexible dual-side single-photon avalanche diode (SPAD) image sensor in arra... more We present the first flexible dual-side single-photon avalanche diode (SPAD) image sensor in array format. The image sensor comprises 32x32 pixels, whereas a special layout and fabrication flow were developed to fabricate the sensor. SPAD breakdown voltage, noise, sensitivity and crosstalk were thoroughly analyzed. The sensor is operated both in frontside-(FSI) and backside-illumination (BSI), whereas a dual-objective camera demo was built to simultaneously demonstrate the sensor in FSI and BSI modes.
A non-linear commercial topology of passive RFID tag is transported onto a low-cost flexible subs... more A non-linear commercial topology of passive RFID tag is transported onto a low-cost flexible substrate by means of antenna embedded distributed decoupling capacitors, which allow to embed both a far-field antenna, operating at 2.4 GHz, and a near-field antenna, operating at 27 MHz, into a compact low-cost layout. The sensor is based on two co-designed planar antennas and a demodulating diode, which receives a two-tone gigahertz signal and radiates back their frequency difference. Filtering elements are embedded directly into the antennas to decouple the near-field and far-field section. The layout transport is realized using silver ink printing on a flexible plastic substrate and can be used for instance as soil moisture sensor when a simple planar capacitance is added to the design. Two-tone measurements of the sensor show the amplitude of the 2nd order intermodulation product at 27 MHz to be only 9 dB lower than the 3rd intermodulation product at 2.400 GHz - 27 MHz, thanks to the high non-linearity of the sensor and the decoupling effect of the distributed capacitors in the metal traces of the folded-slot antenna topology.
Optics Express, Feb 16, 2016
We proposed the world's first flexible ultrathin-body singlephoton avalanche diode (SPAD) as phot... more 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.
2013 IEEE International Electron Devices Meeting, 2013
The world's first flexible ultra-thin-body SOI single-photon avalanche diode (SPAD) is reported w... more The world's first flexible ultra-thin-body SOI single-photon avalanche diode (SPAD) is reported with peak photon detection probability (PDP) at 11%, dark count rate (DCR) around 20kHz and negligible afterpulsing and cross-talk. It compares favorably with CMOS SPADs while it can be bended to 10mm-diameter and operate both in frontside-(FSI) and backside-illumination (BSI).
2011 IEEE International Integrated Reliability Workshop Final Report, 2011
Thin Solid Films, Mar 1, 2003
This paper reviews advanced excimer-laser crystallization techniques, developed by our group, ena... more This paper reviews advanced excimer-laser crystallization techniques, developed by our group, enabling precise location-control of the individual Si grains. Combined microstructure and time-resolved optical reflectivity investigations during conventional excimer-laser crystallization showed that explosive crystallization occurs during excimer-laser irradiation. The location-control methods use local structural modification in the underlying materials (substrate) using a conventional photolithography. With the developed process, the large grains having a diameter of 6 mm can be set precisely at predetermined positions. We will also discuss the performance of the single-crystalline Si TFTs that are formed within the location-controlled Si grains. The field-effect mobility for electrons is 430 cm yV s on average, which is well comparable to that of TFTs made with silicon-on-insulator 2 wafers.
The Japan Society of Applied Physics, Jul 17, 2015
ECS transactions, Aug 5, 2014
Printing is attractive for manufacturing flexible circuits. This manuscript presents our investig... more Printing is attractive for manufacturing flexible circuits. This manuscript presents our investigation of single-grain Si TFTs fabricated from printed liquid-Si, on a polyimide substrate with the maximum process temperature of 350 °C. The field-effect mobility is 460 cm2/Vs for electrons and 121 cm2/Vs for the holes. CMOS inverters were also fabricated. The devices function at the bending diameter of 3 mm. The device performance under the bending stress was discussed.
Springer eBooks, 2001
In this paper we describe a new optical detector system for fluorescence analysis in on-chip high... more In this paper we describe a new optical detector system for fluorescence analysis in on-chip high-speed-screening arrays. It consists of a photodiode covered by a re-crystallized silicon film, which acts as a single-film optical filter. The fabrication is fully compatible with standard CMOS processes. The optical properties of the filter are such that fluorescent light of wavelengths of 420 nm or higher can be measured in the presence of the (UV) excitation light (340–360 nm). A selectivity exceeding 35 dB has been demonstrated. The technique has the potential for 50 dB selectivity and higher. NADH concentration measurements illustrate the application of the system for determination of enzymatic activity of different analytes.
Applied Physics Letters, Apr 10, 2006
応用物理学会春季学術講演会講演予稿集(CD-ROM), 2015
Springer series in materials science, 2014
Pulsed-Laser-induced epitaxial growth (PLEG) is an attractive method for lateral overgrowth of or... more Pulsed-Laser-induced epitaxial growth (PLEG) is an attractive method for lateral overgrowth of orientation-controlled silicon (Si). As underlying MOS-FETs on the seeding crystalline Si wafer is not thermally damaged, the PLEG is promising for monolithic 3D integration of circuits. This paper will review our systematic studies of both simulation and experiment on the PLEG of Si aimed for fundamental understanding of the epitaxial growth and reduction of defect generation. Experimentally a XeCl excimer-laser irradiates the sample which consists of amorphous-silicon (a-Si) deposited on a thick SiO2 with a small contact opening on a 〈100〉 oriented SOI or bulk-Si wafer. The experiment verified our 2D transient heat transfer simulation results that the combination of the long-pulse and the bulk-Si wafer gives the widest process window. The bulk-Si wafer seeding provided the larger Si island size of 6 μm than that of the SOI (4 μm). From Electron Backscattering Diffraction (EBSD) analysis it was found that 〈100〉 is the main surface crystallographic orientation. However there exist four, isolated secondary sub-grains inside the Si island. TEM cross-sectional image revealed formation of the subgrains due to formation of Σ3 (111) type of coincident site lattice (CSL) boundary originated at the SiO2 sidewall. We believe that the gentle slope of the side wall allows the extension of the facet to the CSL boundary and subgrains. At last we introduced a way to reduce the CSL boundary formation in the PLEG of Si. By using 75∘ steep sidewalls of the opening to the seed, we have successfully obtained an array of Si islands having a size of 4 μm with {100} surface orientation only, without any subgrains inside.
ABSTRACT Cited By (since 1996): 1, Export Date: 13 July 2012, Source: Scopus
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Papers by Ryoichi Ishihara