Multiplexing Readout Research Articles

Time-domain multiplexed SQUID readout of a bolometer camera for APEX

We describe the development and fabrication of the sub-millimeter APEX (Atacamapathfinder experiment) bolometer camera (SABOCA) and its installation at the APEXradio telescope in Chile. SABOCA has 37 bolometers for a wavelength of about0.35 mm. The bolometers with superconducting transition-edge sensors are readout by superconducting quantum interference devices (SQUIDs). Time-domainmultiplexing was used to compress 40 readout signals into four output channels, whichare further amplified by superconducting quantum interference filters (SQIF).The multiplexer readout circuit is described in detail. One spare SQUID andtwo spare bolometers have been used as reference to evaluate contributions tothe bolometer noise figure. SABOCA’s electrical noise equivalent power is about7 × 10 − 16 W Hz − 1/2, whereas the optical noise equivalent flux density measured at APEX is better than0.35 Jy Hz − 1/2 (1 Jy = 10 − 26 W m − 2 Hz − 1). The measured bolometer noise exceeds the theoretical estimation by factor of two,possibly caused by excess noise in the transition-edge sensor. Nevertheless theachieved instrumental sensitivity meets the specification given by the APEX board.SABOCA was commissioned as the facility instrument in the spring of 2009.

Sequential Multiplex Analyte Capturing for Phosphoprotein Profiling

Microarray-based sandwich immunoassays can simultaneously detect dozens of proteins. However, their use in quantifying large numbers of proteins is hampered by cross-reactivity and incompatibilities caused by the immunoassays themselves. Sequential multiplex analyte capturing addresses these problems by repeatedly probing the same sample with different sets of antibody-coated, magnetic suspension bead arrays. As a miniaturized immunoassay format, suspension bead array-based assays fulfill the criteria of the ambient analyte theory, and our experiments reveal that the analyte concentrations are not significantly changed. The value of sequential multiplex analyte capturing was demonstrated by probing tumor cell line lysates for the abundance of seven different receptor tyrosine kinases and their degree of phosphorylation and by measuring the complex phosphorylation pattern of the epidermal growth factor receptor in the same sample from the same cavity.

A 1k-pixel CTIA readout multiplexer for far-IR photodetector arrays

SB349 is the first 32 × 32 CTIA readout multiplexer specifically designed for far-IR photodetectors and is operable at cryogenic temperatures at least as low as 1.7 K. Four of these readouts can be butted together to form a 64 × 64 mosaic array. The array is multiplexed into eight parallel outputs and features eight selectable gain settings to accommodate various background levels, auto-zero for better input uniformity, and sample-and-hold circuitry. A special, 2-micron cryo-CMOS process was adopted to prevent freeze out and ensure low noise and proper operation at deep cryogenic temperatures. The read noise of the bare device at 4.2 K and under nominal sampling conditions was measured to be about 250e − for the 106fF signal capacitor with the well capacity of 400ke −. Hybridized to a typical germanium detector, the array should achieve NEP levels in the low 10 –18 W/√Hz. An overview of the design and the latest results of the test and characterization of this device are reported in this paper.

Linearized superconducting quantum interference device array for high bandwidth frequency-domain readout multiplexing

We have designed and demonstrated a superconducting quantum interference device (SQUID) array linearized with cryogenic feedback. To achieve the necessary loop gain, a 300-element series array SQUID is constructed from three monolithic 100-element series arrays. A feedback resistor completes the loop from the SQUID output to the input coil. The short feedback path of this linearized SQUID array (LISA) allows for a substantially larger flux-locked loop bandwidth as compared to a SQUID flux-locked loop that includes a room temperature amplifier. The bandwidth, linearity, noise performance, and 3 Phi(0) dynamic range of the LISA are sufficient for its use in our target application: the multiplexed readout of transition-edge sensor bolometers.

Kinetic Inductance Detectors development for mm-wave Astronomy

Throughout the last decades, development of low-temperat- ure detectors focused mainly on the design of high-sensitivity, single-pixel devices. This includes such devices as semiconductor-based photodetectors and bolometers, Magnetic Metallic Calorimeters (MMC), Superconducting Tunnel Junctions (STJ), and Transition Edge Sensors (TES). However, these devices have had limited success in achieving the simultaneous large-scale array sizes and large-bandwidth operation necessary for high-speed, high-resolution detection. To overcome this performance limitation, it is advisable to focus on low-temperature detectors which are intrinsically adapted to giant-array multiplexing and ultra-fast readout. To adopt large scale frequency-domain multiplexing for low-temperature detectors, it is necessary to find detectors which“broadcast” at microwave frequencies. Superconducting microwave resonators naturally lend themselves to this task. One recent demonstration is an implementation known as Kinetic Inductance Detectors (KIDs). This detection mechanism can be adopted for low-energy EM radiation (radio, mm, THz) in continuous mode, or in pulsed mode for higher energy radiation and particles. We present an ongoing development for a KIDs instrument dedicated to millimetric ground-based observations at the 30m IRAM telescope at Pico Veleta. The Neel IRAM KIDs Array (NIKA) project is coordinated in Grenoble and involves groups in Holland (SRON), UK (Cardiff) and Italy (Roma).

FPGA Electronics for OPET: A Dual-Modality Optical and Positron Emission Tomograph.

The development of a prototype dual-modality optical and PET (OPET) small animal imaging tomograph is underway in the Crump Institute for Molecular Imaging at the University of California Los Angeles. OPET consists of a single ring of six detector modules with a diameter of 3.5 cm. Each detector has an 8 × 8 array of optically isolated BGO scintillators which are coupled to multichannel photomultiplier tubes and open on the front end. The system operates in either PET or optical mode and reconstructs the data sets as 3D tomograms. The detectors are capable of detecting both annihilation events (511 keV) from PET tracers as well as Single Photon Events (SPEs) (2-3 eV) from bioluminescence. Detector channels are readout using a custom multiplex readout scheme and then filtered in analog circuitry using either a γ-ray or SPE specific filter. Shaped pulses are sent to a Digital Signal Processing (DSP) unit for event processing. The DSP unit has 100 MHz Analog-to-Digital Converters on the front-end which send digitized samples to Field Programmable Gate Arrays which are programmed via user configurable algorithms to process PET coincidence events or bioluminescence SPEs. Information determined using DSP includes: event timing, energy determination-discrimination, position determination-lookup, and coincidence processing. Coincidence or SPE events are recorded to an external disk and minimal post processing is required prior to image reconstruction. Initial imaging results from a phantom filled with 18FDG solution and an optical pattern placed on the front end of a detector module in the vicinity of a SPE source are shown.

Indium Hybridization of Large Format TES Bolometer Arrays to Readout Multiplexers for Far-Infrared Astronomy

The advance of new detector technologies combined with enhanced fabrication methods has resulted in an increase in development of large format arrays. The next generation of scientific instruments will utilize detectors containing hundreds to thousands of elements providing a more efficient means to conduct large area sky surveys. Some notable detectors include a 32x32 x-ray microcalorimeter for Constellation-X, an infrared bolometer called SAFIRE to fly on the airborne observatory SOFIA, and the sub-millimeter bolometer SCUBA-2 to be deployed at the JCMT which will use more than 10,000 elements for two colors, each color using four 32x40 arrays. Of these detectors, SCUBA-2 is farthest along in development and uses indium hybridization to multiplexers for readout of the large number of elements, a technology that will be required to enable the next generation of large format arrays. Our current efforts in working toward large format arrays have produced GISMO, the Goddard IRAM Superconducting 2-Millimeter observer. GISMO is a far infrared instrument to be field tested later this year at the IRAM 30 meter telescope in Spain. GISMO utilizes transition edge sensor (TES) technology in an 8x16 filled array format that allows for typical fan-out wiring and wire-bonding to four 1x32 NIST multiplexers. GISMO'S electrical wiring is routed along the tops of 30 micron walls which also serve as the mechanical framework for the array. This architecture works well for the 128 element array, but is approaching the limit for routing the necessary wires along the surface while maintaining a high fill factor. Larger format arrays will benefit greatly from making electrical connections through the wafer to the backside, where they can be hybridized to a read-out substrate tailored to handling the wiring scheme. The next generation array we are developing is a 32x40 element array on a pitch of 1135 microns that conforms to the NIST multiplexer, already developed for the SCUBA-2 instrument This architecture will utilize electrical connections that route from the TES to the support frame and through the wafer. The detector chip will then be hybridized to the NIST multiplexer via indium bump bonding. In our development scheme we are using substrates that allow for diagnostic testing of electrical continuity across the entire array and we are testing our process to minimize or eliminate any contact resistance at metal interfaces. Our goal is hybridizing a fully functional 32x40 array of TES bolometers to a NIST multiplexer. The following work presents our current progress toward enabling this technology.

Ultrathin NbN film superconducting single-photon detector array

We report on the fabrication process of the 2 × 2 superconducting single-photon detector (SSPD) array. The SSPD array is made from ultrathin NbN film and is operated at liquid helium temperatures. Each detector is a nanowire-based structure patterned by electron beam lithography process. The advances in fabrication technology allowed us to produce highly uniform strips and preserve superconducting properties of the unpatterned film. SSPD exhibit up to 30% quantum efficiency in near infrared and up to 1% at 5-μm wavelength. Due to 120 MHz counting rate and 18 ps jitter, the time-domain multiplexing read-out is proposed for large scale SSPD arrays. Single-pixel SSPD has already found a practical application in non-invasive testing of semiconductor very-large scale integrated circuits. The SSPD significantly outperformed traditional single-photon counting avalanche diodes.

Use of quantum-point-contact high-electron-mobility-transistors for time domain multiplexing of large arrays of high impedance low temperature bolometers

The use of a multiplexing readout for an array of bolometers simplifies the electronics and wiring, so making the readout of large arrays of bolometers (>100) feasible. Here we describe a time domain multiplexing technique and its performance based on the use of quantum-point-contact high-electron-mobility-transistors as low temperature (to approximately 100 mK) switches for measuring high impedance (5...70 MOmega) resistances and sensors. The presented system is well matched to ground based millimetric astronomy demands.

A low noise 2 × 16 Ge:Sb focal-plane array: Paving the way for large format FPAs for far IR astronomy

Future astronomical instruments call for large format and high sensitivity far infrared focal-plane arrays to meet their science objectives. Arrays as large as 128 × 128 with sensitivities equal to or better than 10 −18 W/√Hz are set as targets for the far IR instruments to be developed within the next 10 years. These seemingly modest goals present a not-so-modest quantum leap for far IR detector technology whose progress is hampered by a number of complexities; chief among them the development of low noise readouts operating at deep cryogenic temperatures and a viable hybridization scheme suitable for far IR detectors. In an effort to incrementally develop large-format photoconductor arrays, we have fabricated a 2 × 16 Ge:Sb array using the SBRC190 readout – a cryogenic 1 × 32 CTIA readout multiplexer initially developed for SOFIA’s AIRES instrument. In this paper we report the results of the extensive parametric tests performed on this array showing an impressive noise performance of 2.2 × 10 −18 W/√Hz and a DQE of 0.41 despite some design limitations. With such an encouraging performance, this prototype array will serve as a platform for our future developmental effort.

Prototype Parallel Readout System for Position Sensitive PMT Based Gamma Ray Imaging Systems

A parallel prototype readout system that allows digitization and acquisition of 64 or more anode signals from a position sensitive photomultiplier tube (PSPMT) was developed for a miniature hand-held gamma camera. This acquisition system was developed to study the benefits of a digital readout system compared to charge multiplexed techniques such as resistive division. The system was developed using CAMAC instrumentation standard and controlled via a Macintosh Computer. Four 16-channel charge-to-digital conversion (QDC) CAMAC modules were used to digitize individual anode signals from the PSPMT. To maximize the data transfer rate, a list processor module was also added in the system. For acquisition and processing of the digitized data, we used Kmax software from SPARROW. The system provided 99.9% spatial linearity when inter-anode gain correction was applied to list-mode data. Much improved scintillation crystal separation in a flood histogram with 16:1 peak to valley ratio, and higher edge sensitivity was obtained compared to resistive charge multiplexing readout

A monolithic integrated 4 × 4 tin oxide gas sensor array with on-chip multiplexing and differential readout circuits

This paper presents a monolithic 4×4 tin oxide gas sensor array together with on-chip multiplexing and differential read-out circuitry. A robust fabrication process focusing on the integration of the CMOS circuitry and the microelectromechanical systems (MEMS) structure is first described. The gas sensor uses a surface micro-machined micro-hotplate based structure. Platinum is selected as the material of choice for both the micro heater and the sensor’s electrodes, for its good thermal stability and compatibility with the sensing film. Different post-treatments are used to modify the characteristics of the tin oxide gas sensors hence improving the sensor’s selectivity of the overall sensor array. Furthermore, in contrast to the conventional voltage divider read-out technique, a novel differential read-out circuit (DRC) for tin oxide gas sensors is proposed. The DRC applies a constant current to drive the sensor and uses a unit-gain single stage amplifier (inverter) to generate a fully differential output, directly from the voltage drop across the sensor. The output of the DRC is simply proportional to the difference between the voltage on the two electrodes of the sensor but not to the transistor parameters such as mobility and threshold voltage, neither to the supply voltage. The monolithic sensor array and its pre-processing circuitry have been implemented in our in-house 5μm process. Experimental results showed good linearity at the output of the DRC for a wide range of sensor resistance variation (over 20MΩ). The fabricated micro-hotplate sensor array was tested for four target gases. Results show good sensitivity and interesting thermal characteristic leading to only 15.5mW power consumption for 300°C operating temperature.

Frequency-domain readout multiplexing of transition-edge sensor arrays

We have demonstrated frequency-domain readout multiplexing of eight channels for superconducting transition-edge sensor bolometer arrays. The multiplexed readout noise is 6.5 pA/√Hz, well below the bolometer dark noise of 15–20 pA/√Hz. We measure an upper limit on crosstalk of 0.004 between channels adjacent in frequency which meets our design requirement of 0.01. We have observed vibration insensitivity in our frequency-domain multiplexed transition-edge sensors, making this system very attractive for telescope and satellite observations. We also discuss extensions to our multiplexed readout. In particular, we are developing a SQUID flux-locked loop that is entirely cold and collaborating on digital multiplexer technology in order to scale up the number of multiplexed channels.

Backshort-Under-Grid arrays for infrared astronomy

We are developing a kilopixel, filled bolometer array for space infrared astronomy. The array consists of three individual components, to be merged into a single, working unit; (1) a transition edge sensor bolometer array, operating in the milliKelvin regime, (2) a quarter-wave backshort grid, and (3) superconducting quantum interference device multiplexer readout. The detector array is designed as a filled, square grid of suspended, silicon bolometers with superconducting sensors. The backshort arrays are fabricated separately and will be positioned in the cavities created behind each detector during fabrication. The grids have a unique interlocking feature machined into the walls for positioning and mechanical stability. The spacing of the backshort beneath the detector grid can be set from ∼30–300 μm, by independently adjusting two process parameters during fabrication. The ultimate goal is to develop a large-format array architecture with background-limited sensitivity, suitable for a wide range of wavelengths and applications, to be directly bump bonded to a multiplexer circuit. We have produced prototype two-dimensional arrays having 8×8 detector elements. We present detector design, fabrication overview, and assembly technologies.

Antenna-coupled bolometer arrays using transition-edge sensors

We are developing antenna-coupled Transition-Edge Sensor (TES) bolometer arrays for use in measurements of the CMB polarization. TES bolometers have many well-known advantages over conventional bolometers, such as increased speed, linearity, and the existence of readout multiplexers. Antenna-coupled bolometers use an on-chip planar antenna to couple light into the bolometer. The antenna directivity and polarization sensitivity, along with the potential for on-chip band defining filters and channelizing circuits, allow a significant increase in focal plane integration. This eliminates the bulky horns, quasioptical filters, dichroics, and polarizers which might otherwise be needed in a conventional bolometric system. This simplification will ease the construction of receivers with larger numbers of pixels. We report on the fabrication and optical testing of single antenna-coupled bolometer pixels with integrated band defining filters. We will also discuss current progress on fabrication of a bolometer array based on this design.

Frequency-Domain SQUID Multiplexing of Transition-Edge Sensors

We describe our frequency-domain readout multiplexer for transition-edge sensor (TES) bolometers and present measurements of an eight-channel multiplexer. Each sensor is biased with a sinusoidal bias at a distinct frequency. As the sensor absorbs power, it amplitude-modulates its sinusoidal bias. Sensor currents are summed and measured with a single superconducting quantum interference device (SQUID) array. The SQUID array consists of 100 dc-SQUID's in series and is operated with shunt feedback electronics which have a slew rate of 1.210/sup 7/ /spl Phi//sub 0//s. A tuned filter consisting of an inductor and capacitor are placed in series with each sensor to both limit the bandwidth of the Nyquist noise from each sensor and to allow us to bias all multiplexed sensors with a common wire. We place an upper limit on crosstalk between adjacent channels of 0.004, well below our design requirements. Demodulated noise spectra from multiplexed sensors show the expected white noise levels at frequencies above 200 mHz.

Frequency-domain multiplexed readout of transition-edge sensor arrays with a superconducting quantum interference device

We demonstrate an eight-channel frequency-domain readout multiplexer for superconducting transition-edge sensors (TESs). Each sensor is biased with a sinusoidal voltage at a unique frequency. The sensor currents are summed and measured with a single superconducting quantum interference device (SQUID) array. The 100-element SQUID array is operated with shunt feedback electronics that have a slew rate of 1.2×107Φ0∕s at 1MHz. The multiplexer readout noise is 6.5pA∕Hz, which is well below the expected sensor noise of 15pA∕Hz. We measure an upper limit on adjacent channel crosstalk of 0.004, which meets our design requirements. The demodulated noise spectra of multiplexed TESs are white at frequencies down to 200mHz.

Tomographic Small-Animal Imaging Using a High-Resolution Semiconductor Camera.

We have developed a high-resolution, compact semiconductor camera for nuclear medicine applications. The modular unit has been used to obtain tomographic images of phantoms and mice. The system consists of a 64 x 64 CdZnTe detector array and a parallel-hole tungsten collimator mounted inside a 17 cm x 5.3 cm x 3.7 cm tungsten-aluminum housing. The detector is a 2.5 cm x 2.5 cm x 0.15 cm slab of CdZnTe connected to a 64 x 64 multiplexer readout via indium-bump bonding. The collimator is 7 mm thick, with a 0.38 mm pitch that matches the detector pixel pitch. We obtained a series of projections by rotating the object in front of the camera. The axis of rotation was vertical and about 1.5 cm away from the collimator face. Mouse holders were made out of acrylic plastic tubing to facilitate rotation and the administration of gas anesthetic. Acquisition times were varied from 60 sec to 90 sec per image for a total of 60 projections at an equal spacing of 6 degrees between projections. We present tomographic images of a line phantom and mouse bone scan and assess the properties of the system. The reconstructed images demonstrate spatial resolution on the order of 1-2 mm.

MaxPET, a dedicated mammary and axillary region PET imaging system for breast cancer

Presents initial measurements from a high-performance prototype dedicated PET camera (maxPET) designed for mammary and axillary region imaging. The system consists of two 15/spl times/15 cm/sup 2/ planar scintillation detector plates operating in coincidence, with each plate composed of 25 modular detectors. The modular detectors are comprised of a 9/spl times/9 array of 3/spl times/3/spl times/20 mm/sup 3/ lutetium oxyorthosilicate (LSO) detector elements, read out by a position-sensitive photomultiplier tube (PS-PMT). A multiplexing readout scheme is used to reduce the number of readout channels from 200 (4X and 4Y readouts per PS-PMT) to 8 channels per plate. The detectors have a measured intrinsic spatial resolution of 2.3 mm. Over 95% of the 4050 crystals in the system can be identified in flood histograms of the detector plates. The coincidence timing resolution for the entire system is 8.1 ns. A line source phantom was scanned with the system and images reconstructed using focal plane tomography. The estimated resolution in projection images is 4 mm based on profiles taken through the line source phantom images. The goal of the maxPET system will be to aid in breast cancer patient management by assisting in imaging women with dense fibro-glandular breasts, detecting axillary lymph node metastases without surgery, and monitoring chemotherapy effectiveness. Future research on the maxPET system will focus on changes to the electronics to improve count rate performance and timing resolution and the mounting of the detectors on a rotating gantry for tomographic studies.

Gamma-ray imaging using a CdZnTe pixel array and a high-resolution, parallel-hole collimator

The poor performance of current parallel-hole collimators is an impediment to planar high-resolution gamma-ray imaging, even when high-resolution semiconductor detector arrays are available. High-resolution parallel-hole collimators are possible but have not been fabricated because conventional collimator construction techniques severely limit achievable bore size and septal thickness. We describe development and testing of a high-resolution collimator with 4096 260-/spl mu/m square bores and 380 /spl mu/-m pitch, matched to our existing 2.5 cm/spl times/2.5 cm hybrid 64/spl times/64 CdZnTe arrays with multiplexer readout. The collimator is a laminar composite of about 100 layers of W sheets produced by photolithography and has an efficiency of 5/spl times/10/sup -5/. We have demonstrated sub-millimeter spatial resolution at 140 keV in both phantom and animal imaging using this system. We present images of resolved individual vertebrae in the spine of a mouse and lymphatic channels and nodes in a rat. The collimator and semiconductor array could form a compact module for use in a wide variety of gamma-ray imaging systems.