Showing papers by "Robert Henderson published in 2012"

Visible-Light Communications Using a CMOS-Controlled Micro-Light- Emitting-Diode Array

Abstract: We report the high-frequency modulation of individual pixels in 8 × 8 arrays of III-nitride-based micro-pixellated light-emitting diodes, where the pixels within the array range from 14 to 84 μ m in diameter. The peak emission wavelengths of the devices are 370, 405, 450 and 520 nm, respectively. Smaller area micro-LED pixels generally exhibit higher modulation bandwidths than their larger area counterparts, which is attributed to their ability to be driven at higher current densities. The highest optical -3 dB modulation bandwidths from these devices are shown to be in excess of 400 MHz, which, to our knowledge, are the highest bandwidths yet reported for GaN LEDs. These devices are also integrated with a complementary metal-oxide-semiconductor (CMOS) driver array chip, allowing for simple computer control of individual micro-LED pixels. The bandwidth of the integrated micro-LED/CMOS pixels is shown to be up to 185 MHz; data transmission at bit rates up to 512 Mbit/s is demonstrated using on-off keying non return-to-zero modulation with a bit-error ratio of less than 1 × 10-10, using a 450 nm-emitting 24 μm diameter CMOS-controlled micro-LED. As the CMOS chip allows for up to 16 independent data inputs, this device demonstrates the potential for multi-Gigabit/s parallel data transmission using CMOS-controlled micro-LEDs.

A Time-Resolved, Low-Noise Single-Photon Image Sensor Fabricated in Deep-Submicron CMOS Technology

Abstract: We report on the design and characterization of a novel time-resolved image sensor fabricated in a 130 nm CMOS process. Each pixel within the 3232 pixel array contains a low-noise single-photon detector and a high-precision time-to-digital converter (TDC). The 10-bit TDC exhibits a timing resolution of 119 ps with a timing uniformity across the entire array of less than 2 LSBs. The differential non-linearity (DNL) and integral non-linearity (INL) were measured at ±0.4 and ±1.2 LSBs, respectively. The pixel array was fabricated with a pitch of 50 μm in both directions and with a total TDC area of less than 2000 μm2. The target application for this sensor is time-resolved imaging, in particular fluorescence lifetime imaging microscopy and 3D imaging. The characterization shows the suitability of the proposed sensor technology for these applications.

A High-Performance Single-Photon Avalanche Diode in 130-nm CMOS Imaging Technology

Abstract: A single-photon avalanche diode (SPAD) is reported in a 130-nm CMOS imaging process which achieves a peak photon detection efficiency (PDE) of ≈72% at 560 nm with >; 40% PDE from 410 to 760 nm. This is achieved by eliminating junction isolation, utilizing dielectric stack optimizations designed for CMOS imaging, and operating at high bias enabled by ac coupling. The 8-μm-diameter device achieves a low median dark count rate of 18 Hz at 2-V excess bias (VEB), a <; 60-ps FWHM timing resolution at 654 nm from VEB = 6 V to VEB = 12 V, and a <; 4% after-pulsing probability. This represents performance which is comparable to fully customized discrete SPADs.

A Single-Photon Avalanche Diode in 90-nm CMOS Imaging Technology With 44% Photon Detection Efficiency at 690 nm

Abstract: A CMOS and back-side illumination-compatible single-photon avalanche diode (SPAD) is reported in 90-nm imaging technology with a peak photon detection efficiency of ≈ 44% at 690 nm and better than ≈20% at 850 nm. This represents an approximately eightfold improvement in near infrared sensitivity over existing CMOS SPADs. This result has important implications for optical communications, time-of-flight ranging, and optical tomography applications. The 6.4-μm-diameter SPAD also achieves the following: low dark count rates of ≈100 Hz with ≈51-ps FWHM timing resolution and a low after-pulsing probability of ≈0.375%.

A High-Throughput Time-Resolved Mini-Silicon Photomultiplier With Embedded Fluorescence Lifetime Estimation in 0.13 $\mu$ m CMOS

Abstract: We describe a miniaturized, high-throughput, time-resolved fluorescence lifetime sensor implemented in a 0.13 m CMOS process, combining single photon detection, multiple channel timing and embedded pre-processing of fluorescence lifetime estimations on a single device. Detection is achieved using an array of single photon avalanche diodes (SPADs) arranged in a digital silicon photomultiplier (SiPM) architecture with 400 ps output pulses and a 10% fill-factor. An array of time-to-digital converters (TDCs) with ≈50 ps resolution records up to 8 photon events during each excitation period. Data from the TDC array is then processed using a centre-of-mass method (CMM) pre-calculation to produce fluorescence lifetime estimations in real-time. The sensor is believed to be the first reported implementation of embedded fluorescence lifetime estimation. The system is demonstrated in a practical laboratory environment with measurements of a variety of fluorescent dyes with different single exponential lifetimes, successfully showing the sensor's ability to overcome the classic pile-up limitation of time-correlated single photon counting (TCSPC) by over an order of magnitude.

Time-domain fluorescence lifetime imaging techniques suitable for solid-state imaging sensor arrays

Abstract: We have successfully demonstrated video-rate CMOS single-photon avalanche diode (SPAD)-based cameras for fluorescence lifetime imaging microscopy (FLIM) by applying innovative FLIM algorithms. We also review and compare several time-domain techniques and solid-state FLIM systems, and adapt the proposed algorithms for massive CMOS SPAD-based arrays and hardware implementations. The theoretical error equations are derived and their performances are demonstrated on the data obtained from 0.13 μm CMOS SPAD arrays and the multiple-decay data obtained from scanning PMT systems. In vivo two photon fluorescence lifetime imaging data of FITC-albumin labeled vasculature of a P22 rat carcinosarcoma (BD9 rat window chamber) are used to test how different algorithms perform on bi-decay data. The proposed techniques are capable of producing lifetime images with enough contrast.

Colloidal quantum dot nanocomposites for visible wavelength conversion of modulated optical signals

Abstract: We report on the steady-state and optical modulation characteristics of a luminescence down-converting colloidal quantum dot/polyimide nanocomposite system suitable for integration with gallium nitride optoelectronics. The approach provides solution-processable and environmentally stable composite materials whose optical conversion and intrinsic modulation properties were evaluated at wavelengths from 535 to 624 nm. A nanocomposite for white-light generation upon excitation and mixing with 450-nm light was also obtained by blending colloidal quantum dots of different sizes in the same matrix. The forward external quantum efficiencies of the resulting nanocomposites were found to depend on the wavelength and can be as high as 33%. Optical modulation bandwidth above 25 MHz, which is an order of magnitude higher than for typical phosphor-based color-converters for GaN LEDs, and wavelength-converted data with an open-eye diagram at 25 Mb/s are demonstrated under external gallium nitride light-emitting diode excitation. These modulation characteristics are correlated with carrier lifetimes. This work provides guideline parameters and creates a possible path to integrated hybrid visible light sources for scientific and communications applications.

CMOS-Controlled Color-Tunable Smart Display

Abstract: We demonstrate a color-tunable smart display system based on a micropixelated light-emitting diode $(\mu\hbox{LED})$ array made from one InGaN epitaxial structure with high (0.4) indium mole fraction. When integrated with custom complementary metal–oxide–semiconductor (CMOS) electronics and a CMOS driving board with a field-programmable gate array (FPGA) configuration, this $\mu\hbox{LED}$ device is computer controllable via a simple USB interface and is capable of delivering programmable dynamic images with emission colors changeable from red to green by tailoring the current densities applied to the $\mu\hbox{LED}$ pixels. The color tunability of this CMOS-controlled device is attributed to the competition between the screening of piezo-electric field and the band filling effect. Comparable brightness of the $\mu\hbox{LED}$ pixels emitting at different colors was achieved by adjusting the duty cycle. Further measurement suggests that this microdisplay system can also be used for high-speed visible light communications.

A reconfigurable 14-bit 60GPhoton/s Single-Photon receiver for visible light communications

Abstract: A reconfigurable Single-Photon Avalanche Diode integration mode receiver in 130nm CMOS is presented for optical links with an array readout bandwidth of 100MHz. The all-digital 32×32 SPAD array achieves a minimum dead time of 5.9ns, and a median dark count rate of 2.5kHz per SPAD. Pulse shortening increases the dynamic range by preventing pulse overlap. An in-pixel feedback loop allows synchronous or self-clocked asynchronous time division multiplexing. The internal gain of SPADs and spatio-temporal summation removes the need for analogue amplification. A maximum count rate of 58GHz is observed, with SNR of 79dB, a sensitivity of −31.7dBm at 100MHz and a BER of 10−9. The sensor core draws 89mW at maximum count rate.

Sub-Micron Lithography Using InGaN Micro-LEDs: Mask-Free Fabrication of LED Arrays

Abstract: The fabrication of gallium-nitride (GaN)-based light-emitting diode (LED) arrays by a direct writing technique, itself using micron-sized LEDs (micro-LEDs), is reported. CMOS-driven ultraviolet GaN-based micro-LED arrays are used to pattern photoresist layers with feature sizes as small as 500 nm. Checkerboard-type square LED array devices are then fabricated using such photoresist patterns based on either single pixel or multipixel direct writing, and implemented as part of a completely mask-less process flow. These exemplar arrays are composed of either 450-nm-emitting 199 $\,\times\,$ 199 $\mu{\rm m}^{2}$ pixels on a 200- $\mu{\rm m}$ pitch or 520-nm-emitting 21 $\,\times\,$ 18 $\mu{\rm m}^{2}$ pixels on a 23- $\mu{\rm m}$ pitch. Fill factors of 99% and 71.5% are achieved with optical output power densities per pixel of 5 and 20 ${\rm W}/{\rm cm}^{2}$ at 90- and 6-mA dc-injected currents, respectively.

A silicon photomultiplier with >30% detection efficiency from 450–750nm and 11.6μm pitch NMOS-only pixel with 21.6% fill factor in 130nm CMOS

Abstract: A 16×16 Silicon Photomultiplier (SiPM) is reported in a 130nm CMOS imaging technology with a photon detection probability of >30% from 450–750nm. The SiPM demonstrates a 21.6% fill factor with an 11.6μm pitch and 8μm diameter SinglePhoton Avalanche Diodes (SPADs). This is achieved using a new SPAD structure with integrated resistor and capacitor. NMOS-only pixel electronics are used to improve fill factor and to implement an addressable array of SPADs that are isolated from the array and column load. A 1T DRAM in each pixel is implemented to inhibit the output of high dark count rate (DCR) SPADs. The SiPM also achieves: a median DCR of ≈200Hz at 1.2V excess bias; low after pulsing; and a SPAD timing jitter of ≈95ps at 654nm with a column delay of ≈100–200ps.

High fill factor digital Silicon Photomultiplier structures in 130nm CMOS imaging technology

Abstract: This paper discusses recent progress in the realization of fully digital Silicon Photomultipliers (SiPMs) in an advanced 130nm CMOS imaging process A dedicated electrical/optical crosstalk characterization chip is reported, featuring a 16×16 SPAD SiPM with on-chip quench, SPAD enable/disable and readout circuitry positioned outside the SPAD array Recent advances in well sharing are employed to deliver a fill factor of 38% Integral crosstalk of <;2% was measured between a SPAD and its neighbors - the lowest yet reported for a high fill factor SiPM structure - measured using parallel readout channels allowing adjacent SPAD waveforms to be monitored in real time

Size effect on efficiency droop of blue light emitting diode

Abstract: In this paper, the size effects on the efficiency droop (ED) in blue InGaN/GaN quantum well light emitting diode are investigated. The smaller size LEDs can work well under much higher power density, especially when the size is reduced to under 40 micro-meters. It shows a weaker ED in these small LEDs. Time correlated single photon counting (TCSPC) measurements show a longer electroluminescence lifetime for smaller size LEDs, which implicates the nonradiative recombination is reduced. It is likely due to Aguer recombination reduction by quantum well (QW) band flatened with the device size decreasing. Cathodoluminescence results indicates that the strain in QWs is relaxed both in the whole pillar and along radial direction of the pillar. The better performance of the smaller size LED is likely attributed to strain relaxation (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Multi-mode photodetector

Abstract: A photodetector includes a photodiode and output circuitry coupled to the photodiode. The photodetector is configurable for operation in at least two modes. A first configurable mode operates the photodetector as an integrating sensor. In this first mode, a bias voltage across the photodiode is set below the breakdown voltage of the photodiode and the output circuitry is configured to read an analog integration output voltage from the photodiode. A second configurable mode operates the photodetector as a single photon avalanche detector. In this second mode, the bias voltage across the photodiode is set above the breakdown voltage of the photodiode and the output circuitry is configured to read an avalanche output voltage.

High-speed GaN micro-LED arrays for data communications

Abstract: We report the modulation performance of micro-light-emitting diode arrays with peak emission ranging from 370 to 520 nm, and emitter diameters ranging from 14 to 84 μm. Bandwidths in excess of 400 MHz and error-free data transmission up to 1.1Gbit/s is shown. These devices are shown integrated with electronic drivers, allowing convenient control of individual array emitters. Transmission using such a device is shown at 512 Mbit/s.

Directly color-tunable smart display based on a CMOS-controlled micro-LED array

Abstract: We demonstrate a CMOS-controlled color-tunable micro-display system based on a micro-light emitting diode array made from one InGaN epitaxial structure. This system can also be used for high speed optical data transmission.

High-bandwidth parallel data transmission using GaN/CMOS micro-LED arrays

Abstract: A multiple-channel visible light communication demonstration system is realized through a CMOS-controlled micro light-emitting diode (μLED) array. A total data transmission rate of 1.5 Gbit/s is achieved by modulating four μLED pixels simultaneously.

A single electron bipolar avalanche transistor implemented in 90 nm CMOS

Abstract: A Single Electron Bipolar Avalanche Transistor (SEBAT) with attoampere sensitivity and ≈10 Hz off-count rate is successfully integrated into 90 nm CMOS. The reported SEBAT has 120 dB (10 Hz–10 MHz) dynamic range corresponding to 0–0.35 VBE, and an IE ≈10−18–10−12 A. Single-transistor ADC operation of the SEBAT is demonstrated by AC-coupling signals into the base.

A gate Modulated avalanche bipolar transistor in 130nm CMOS technology

Abstract: A novel Geiger-mode avalanche bipolar transistor structure is realized in a 130nm, low-voltage CMOS technology. A MOS transistor formed within the base region of the device allows gate modulation of the output pulse rate. In bipolar operation, the device generates Poisson-distributed digital output pulses at rates from 1kHz to 20MHz, linearly related to emitter currents in the range 10nA to 1μA. In MOS operation, the mean pulse rate varies exponentially over 4–5 decades as the gate voltage changes by 300mV and consumes less than 180μA drain-source current. The gate input eliminates the input current of the avalanche bipolar transistor, enabling capacitive sensor interfaces and direct device-level, analogue-digital conversion. The device is fully compatible with low-voltage CMOS circuits and standard digital process steps.

High speed GaN micro-light-emitting diode arrays for data communications

Abstract: Micro light-emitting diode (micro-LED) arrays based on an AlInGaN structure have attracted much interest recently as light sources for data communications. Visible light communication (VLC), over free space or plastic optical fibre (POF), has become a very important technique in the role of data transmission. The micro-LEDs which are reported here contain pixels ranging in diameter from 14 to 84μm and can be driven directly using a high speed probe or via complementary metal-oxide semiconductor (CMOS) technology. The CMOS arrays allow for easy, computer control of individual pixels within arrays containing up to 16×16 elements. The micro-LEDs best suited for data transmission have peak emissions of 450nm or 520nm, however various other wavelengths across the visible spectrum can also be used. Optical modulation bandwidths of over 400MHz have been achieved as well as error-free (defined as an error rate of <1x10-10) data transmission using on-off keying (OOK) non-return-to-zero (NRZ) modulation at data rates of over 500Mbit/s over free space. Also, as a step towards a more practical multi-emitter data transmitter, the frequency response of a micro-LED integrated with CMOS circuitry was measured and found to be up to 185MHz. Despite the reduction in bandwidth compared to the bare measurements using a high speed probe, a good compromise is achieved from the additional control available to select each pixel. It has been shown that modulating more than one pixel simultaneously can increase the data rate. As work continues in this area, the aim will be to further increase the data transmission rate by modulating more pixels on a single device to transmit multiple parallel data channels simultaneously.

P-142L: Late-News Poster: Time of Flight Based 3D Image Sensing Using Holographically Projected Structured Illumination

Abstract: A novel Time of Flight based 3D imaging system incorporates adaptive structured illumination using holographic projection via a phase-modulating ferroelectric liquid crystal on silicon spatial light modulator. It demonstrates high optical signal to noise ratio and low optical cross-talk.