Analysis and comparison of resistive, ferroelectric and pyroelectric uncooled bolometers for electronic imaging systems

The performance parameters (responsivity (Rv). detectivity (D*), total noise and response time) of resistive, pyroelectric and ferroelectric bolometer detectors are dependent on a large number of key variables including chopping frequercy, the input impedance and voltage noise of the readout circuitry, the structure dependent parameters (particularly thermal conductance and thermal capacitance), and material properties such as dielectric constant, pyroelectric coefficient, loss tangent and thin film thickness. The interrelationship between the key variables and their influence on performance is often complex and not easily discerned for the three major types of thermal detectors: resistive, pyroelectric and ferroelectric bolometers. In this thesis research, the dependence of Rv, D* and total noise on these key parameters were analyzed and written as equations from which computer calculations could easily be made. The analyzed results were used to compare the pertbrmance of the three types of sensors for present-day structure and material characteristics and also for material characteristics and structures that night be developed in the future

Конструкция и характеристики неохлаждаемых болометрических инфракрасных решеток на основе аморфного кремния

Uncooled bolometric type thermal detectors, combined into a matrix and placed into a focal plane array have the following characteristics: low cost, operation at room temperature, compatibility with the silicon CMOS technology, and high detecting performance; therefore recently it became a hot spot in infrared or terahertz detection field. The performance of uncooled infrared focal plane detector arrays depends on the optimization of critical parameters which are determined by geometrical design and the electrical, optical, and thermal physical properties of the detector materials. We report the study of a fabrication process and characterization of two (2D) dimensional arrays of uncooled microbolometers based on silicon (α-Si) thermo-sensing films. Because these arrays substantially reduce sensor size, they are becoming the preferred format for most modern applications. Неохлаждаемые тепловые детекторы болометрического типа, объединенные в матрицу, размещенную в фокальной плоскости, в последнее время активно применяются в инфракрасном или терагерцовом поле обнаружения, поскольку обладают низкой стоимостью и высокой эффективностью обнаружения, совместимы с кремниевой КМОП-технологией, а также работают при комнатной температуре. Характеристики таких детекторов зависят от оптимизации критических параметров, которые определяются геометрической конструкцией, электрическими, оптическими и тепловыми свойствами применяемых материалов. В статье рассмотрены эксплуатационные характеристики пикселей двумерных массивов неохлаждаемых микроболометров на основе термочувствительных пленок аморфного кремния. Поскольку эти массивы значительно уменьшают размер сенсора, они становятся предпочтительным форматом для большинства современных приложений.

Low-power CMOS digital-pixel Imagers for high-speed uncooled PbSe IR applications

This PhD dissertation describes the research and development of a new low-cost medium wavelength infrared MWIR monolithic imager technology for high-speed uncooled industrial applications. It takes the baton on the latest technological advances in the field of vapour phase deposition (VPD) PbSe-based medium wavelength IR (MWIR) detection accomplished by the industrial partner NIT S.L., adding fundamental knowledge on the investigation of novel VLSI analog and mixed-signal design techniques at circuit and system levels for the development of the readout integrated device attached to the detector. The work supports on the hypothesis that, by the use of the preceding design techniques, current standard inexpensive CMOS technologies fulfill all operational requirements of the VPD PbSe detector in terms of connectivity, reliability, functionality and scalability to integrate the device. The resulting monolithic PbSe-CMOS camera must consume very low power, operate at kHz frequencies, exhibit good uniformity and fit the CMOS read-out active pixels in the compact pitch of the focal plane, all while addressing the particular characteristics of the MWIR detector: high dark-to-signal ratios, large input parasitic capacitance values and remarkable mismatching in PbSe integration. In order to achieve these demands, this thesis proposes null inter-pixel crosstalk vision sensor architectures based on a digital-only focal plane array (FPA) of configurable pixel sensors. Each digital pixel sensor (DPS) cell is equipped with fast communication modules, self-biasing, offset cancellation, analog-to-digital converter (ADC) and fixed pattern noise (FPN) correction. In-pixel power consumption is minimized by the use of comprehensive MOSFET subthreshold operation. The main aim is to potentiate the integration of PbSe-based infra-red (IR)-image sensing technologies so as to widen its use, not only in distinct scenarios, but also at different stages of PbSe-CMOS integration maturity. For this purpose, we posit to investigate a comprehensive set of functional blocks distributed in two parallel approaches: • Frame-based “Smart” MWIR imaging based on new DPS circuit topologies with gain and offset FPN correction capabilities. This research line exploits the detector pitch to offer fully-digital programmability at pixel level and complete functionality with input parasitic capacitance compensation and internal frame memory. • Frame-free “Compact”-pitch MWIR vision based on a novel DPS lossless analog integrator and configurable temporal difference, combined with asynchronous communication protocols inside the focal plane. This strategy is conceived to allow extensive pitch compaction and readout speed increase by the suppression of in-pixel digital filtering, and the use of dynamic bandwidth allocation in each pixel of the FPA. In order make the electrical validation of first prototypes independent of the expensive PbSe deposition processes at wafer level, investigation is extended as well to the development of affordable sensor emulation strategies and integrated test platforms specifically oriented to image read-out integrated circuits. DPS cells, imagers and test chips have been fabricated and characterized in standard 0.15μm 1P6M, 0.35μm 2P4M and 2.5μm 2P1M CMOS technologies, all as part of research projects with industrial partnership. The research has led to the first high-speed uncooled frame-based IR quantum imager monolithically fabricated in a standard VLSI CMOS technology, and has given rise to the Tachyon series [1], a new line of commercial IR cameras used in real-time industrial, environmental and transportation control systems. The frame-free architectures investigated in this work represent a firm step forward to push further pixel pitch and system bandwidth up to the limits imposed by the evolving PbSe detector in future generations of the device.La present tesi doctoral descriu la recerca i el desenvolupament d'una nova tecnologia monolítica d'imatgeria infraroja de longitud d'ona mitja (MWIR), no refrigerada i de baix cost, per a usos industrials d'alta velocitat. El treball pren el relleu dels últims avenços assolits pel soci industrial NIT S.L. en el camp dels detectors MWIR de PbSe depositats en fase vapor (VPD), afegint-hi coneixement fonamental en la investigació de noves tècniques de disseny de circuits VLSI analògics i mixtes pel desenvolupament del dispositiu integrat de lectura unit al detector pixelat. Es parteix de la hipòtesi que, mitjançant l'ús de les esmentades tècniques de disseny, les tecnologies CMOS estàndard satisfan tots els requeriments operacionals del detector VPD PbSe respecte a connectivitat, fiabilitat, funcionalitat i escalabilitat per integrar de forma econòmica el dispositiu. La càmera PbSe-CMOS resultant ha de consumir molt baixa potència, operar a freqüències de kHz, exhibir bona uniformitat, i encabir els píxels actius CMOS de lectura en el pitch compacte del pla focal de la imatge, tot atenent a les particulars característiques del detector: altes relacions de corrent d'obscuritat a senyal, elevats valors de capacitat paràsita a l'entrada i dispersions importants en el procés de fabricació. Amb la finalitat de complir amb els requisits previs, es proposen arquitectures de sensors de visió de molt baix acoblament interpíxel basades en l'ús d'una matriu de pla focal (FPA) de píxels actius exclusivament digitals. Cada píxel sensor digital (DPS) està equipat amb mòduls de comunicació d'alta velocitat, autopolarització, cancel·lació de l'offset, conversió analògica-digital (ADC) i correcció del soroll de patró fixe (FPN). El consum en cada cel·la es minimitza fent un ús exhaustiu del MOSFET operant en subllindar. L'objectiu últim és potenciar la integració de les tecnologies de sensat d'imatge infraroja (IR) basades en PbSe per expandir-ne el seu ús, no només a diferents escenaris, sinó també en diferents estadis de maduresa de la integració PbSe-CMOS. En aquest sentit, es proposa investigar un conjunt complet de blocs funcionals distribuïts en dos enfocs paral·lels: - Dispositius d'imatgeria MWIR "Smart" basats en frames utilitzant noves topologies de circuit DPS amb correcció de l'FPN en guany i offset. Aquesta línia de recerca exprimeix el pitch del detector per oferir una programabilitat completament digital a nivell de píxel i plena funcionalitat amb compensació de la capacitat paràsita d'entrada i memòria interna de fotograma. - Dispositius de visió MWIR "Compact"-pitch "frame-free" en base a un novedós esquema d'integració analògica en el DPS i diferenciació temporal configurable, combinats amb protocols de comunicació asíncrons dins del pla focal. Aquesta estratègia es concep per permetre una alta compactació del pitch i un increment de la velocitat de lectura, mitjançant la supressió del filtrat digital intern i l'assignació dinàmica de l'ample de banda a cada píxel de l'FPA. Per tal d'independitzar la validació elèctrica dels primers prototips respecte a costosos processos de deposició del PbSe sensor a nivell d'oblia, la recerca s'amplia també al desenvolupament de noves estratègies d'emulació del detector d'IR i plataformes de test integrades especialment orientades a circuits integrats de lectura d'imatge. Cel·les DPS, dispositius d'imatge i xips de test s'han fabricat i caracteritzat, respectivament, en tecnologies CMOS estàndard 0.15 micres 1P6M, 0.35 micres 2P4M i 2.5 micres 2P1M, tots dins el marc de projectes de recerca amb socis industrials. Aquest treball ha conduït a la fabricació del primer dispositiu quàntic d'imatgeria IR d'alta velocitat, no refrigerat, basat en frames, i monolíticament fabricat en tecnologia VLSI CMOS estàndard, i ha donat lloc a Tachyon, una nova línia de càmeres IR comercials emprades en sistemes de control industrial, mediambiental i de transport en temps real.Postprint (published version

A highly digital microbolometer ROIC employing a novel event-based readout and two-step time to digital converters

Uncooled infrared imaging systems are a light weight and low cost alternative to their cooled counterparts. Uncooled microbolometer IR focal plane arrays (IRFPAs) for applications such as medical imaging, thermography, night vision, surveillance and industrial process control have recently been under focus. These systems have small pixel pitches ( 250 K). Low NETD demands excellent microbolometer and readout noise performance. If sensitive analog circuits, driving long metal interconnects, are part of the predigitization readout channel, this necessitates the use of power consuming buffers, potentially in conjunction with noise cancellation circuits that result in power and area overhead. Thus re-thinking at the architectural level is crucial to meet these demands. Accordingly, in this thesis a column-parallel readout architecture for frame synchronous microbolometer imagers is proposed that enables low power operation by employing a time mode digitizer. The proposed readout circuit is based on a bridge type detector network with active and reference microbolometers and employs a capacitive transimpedance amplifier (CTIA) incorporating a novel two-step integration mechanism. By using a modified reset scheme in the CTIA, a forward ramp is initiated at the input side followed by the conventional backward integrated ramp at the output. This extends the measurement interval and improves signal-to-noise ratio (SNR). A synchronous counter based TDC measures this interval providing robust digitization. This technique also provides a way of compensating for self-heating effects. Being highly digital, the proposed architecture offers robust frontend processing and achieves a per channel power consumption of 66 µW, which is considerably lower than the most recently reported designs, while maintaining better than 10mK readout NETD

Protein Impregnated Polymer (PIP) Film Infrared Sensor Using Suspended Microelectromechanical Systems (MEMS) Pixels

The Air Force Research Laboratory Materials and Manufacturing Directorate have developed a novel protein impregnated polymer (PIP) suspension that changes resistivity as a function of absorbed infrared radiation. Due to this property, the PIP is a potential material for use as an uncooled bolometer, or thermal sensor. In this research, a thermally-isolated pixel design, sensor characterization methods, and sensor fabrication and processing steps were developed. To create a microbolometer, the PIP was applied to two prototype micro-electro-mechanical systems (MEMS) surface micro-machined structures. The first is a raised cantilever pixel array that uses residual stress polysilicon and metal film arms to bend the pixels away from their substrate. The second is a suspended membrane pixel array in which the backside silicon wafer substrate is removed. The thermal sensor\u27s figures of merit responsivity, detectivity, noise equivalent power, noise equivalent temperature difference, and thermal time constant, were modeled. An attempt was made to evaluate the performance of the fabricated microbolometer pixels by comparing measured data to model predictions. This research shows the PIP material can be used to make a practical thermal sensor

High Power Quantum Cascade Laser for Terahertz Imaging

Video rate or real-time imaging in the terahertz (THz) frequency range has become possible in the last few years with the advent of compact and high power THz sources, such as quantum cascade (QC) lasers, and the THz-sensitive vanadium oxide based microbolometer focal plane arrays. A new higher power QCL had been acquired and was characterized using FTIR spectroscopic techniques as part of this thesis. Spectral analysis revealed the center radiation frequency to be about 3.78 THz, which was close to the manufacturers specification. Relative power analysis showed significantly higher magnitude, of at least two orders, than the previous low power QCL. Significant temperature build-up of the cryostat, where the laser was mounted, was noticed in terms of a temperature rise of about 16 Kelvins, but was not detrimental to the laser performance. Active real-time THz imaging was conducted with the laser and a 160 x 120 element microbolometer focal plane array camera, FLIR A20M. The off-axis parabolic (OAP) reflective mirrors were re-configured for the imaging experiment to ensure sufficient THz energy would be focused onto the object. This optical setup could be easily re-configured for either transmission mode, as well as reflective mode imaging experiments. A synchronization circuitry was designed to synchronously modulate the QCL pulses with the focal plane array for differential imaging. This operation would eliminate unwanted signals from the infrared background, obviating the need for dedicated spectral filters that would have significantly attenuated the THz signal as well. Preliminary experiments showed better contrast in the acquired images. Post-processing algorithms such as addition of digital gain, enhanced edges, and integration of multiple images could potentially enhance the quality of the THz images, and extend the research towards reflective and stand-off THz imaging.http://archive.org/details/highpowerquantum109456845Civilian, DSO National Laboratories, Singapor

Shape Memory Polymer Resonators as Highly Sensitive Uncooled Infrared Detectors

Uncooled InfraRed (IR) detectors have enabled the rapid growth of thermal imaging applications. These detectors are predominantly bolometers, where the heating of pixel from incoming IR radiation is read out as a resistance change. Another uncooled sensing method is to transduce the IR radiation into the frequency shift of a mechanical resonator. We present here a highly sensitive, simple to fabricate resonant IR sensor, based on thermo-responsive Shape Memory Polymers (SMPs). By exploiting the phase-change polymer as the transduction mechanism, our approach provides 2 orders of magnitude improvement of the temperature coefficient of frequency (TCF). The SMP has very good absorption in IR wavelengths, obviating the need for an absorber layer. A Noise Equivalent Temperature Difference (NETD) of 22 mK in vacuum and 112 mK in air are obtained using f/2 optics. Such high performance in air eliminates the need for vacuum packaging, paving a path towards flexible IR sensors

Uncooled Infrared Detector Featuring Silicon based Nanoscale Thermocouple

The main focus of this dissertation is to improve the performance of thermoelectric (TE) infrared (IR) detectors. TE IR detectors are part of uncooled detectors that can operate at room temperature. These detectors have been around for many years, however, their performance has been lower than their contesting technologies. A novel high-responsivity uncooled thermoelectric infrared detector is designed, fabricated, and characterized. This detector features a single standalone polysilicon-based thermocouple (without a supporting membrane) covered by an umbrellalike optical-cavity IR absorber. It is proved that the highest responsivity in the developed detectors can be achieved with only one thermocouple. Since the sub-micrometer polysilicon TE wires are the only heat path from the hot junction to the substrate, a superior thermal isolation is achieved. A responsivity of 1800 V/W and a detectivity of 2 ? 10^8 (cm. sqrt(Hz)W^?1) are measured from a 20?m x 20?m detector comparable to the performance of detectors used in commercial focal planar arrays. This performance in a compact and manufacturable design elevates the position of thermoelectric IR sensors as a candidate for low-power, high performance, and inexpensive focal planar arrays. The improvement in performance is mostly due to low thermal conductivity of thin polysilicon wires. A feature is designed and fabricated to characterize the thermal conductivity of such a wire and it is shown for the first time that the thermal conductivity of thin polysilicon films can be much lower than that of the bulk. Thermal conductivity of ~110nm LPCVD polysilicon deposited at 620C is measured to be ~3.5W/m.K

Status of Cooled and Uncooled Infrared Detectors at SCD, Israel

For the highest end mid-wave-infrared (MWIR) applications, SCD offers a family of cryogenically cooled detectors with background limited performance (BLIP). The matured InSb planar technology is implemented in a variety of focal plane arrays, from a 320 x 256 format with a 30 µm pitch to a 1280 x 1024 format with a 15 µm pitch, all of which are operated at 77K. A major challenge is to reduce the cooling requirements. Then substantial reductions in size, weight, and power (SWaP) can be achieved by using a smaller cooler and Dewar assembly. SCD’s new epi-InSb detectors, grown by molecular beam epitaxy (MBE), have a BLIP temperature of ~100 K at F/3. This enhanced operating temperature reduces the required cooling power by ~20 % compared with the conventional 77 K operation. For a very high operating temperature, we have developed the new XBn-InAsSb detector with a 4.2 µm cut-off wavelength. This detector exhibits a BLIP temperature of ~160K at F/3 and a reduction in cooling power of ~60 %. These HOT detectors enable an improved range of solutions, including faster cool-down time and mission readiness, longer mission times, and higher cooler reliability. We can also exploit their reduced dark current to obtain an enhanced signal to noise ratio at lower operating temperatures.  The well-established 25 µm pitch family of uncooled µ-Bolometer detector has two basic formats, 384 x 288 and 640 x 480, and several sensitivity grades. The very high sensitivity 25 µm pitch detector has been demonstrated at F/2.4 for mid-range systems. The wide-band detector is optimized for both the long-wave-infrared and mid-wave-infrared spectral bands. Recently we developed the new 17 µm pitch family of detectors. The 640x480 format is a leading candidate for applications such as thermal weapon sights, driver vision enhancers and other mid-range IR systems. The 17 µm family is currently being expanded with the high sensitivity grade and with the addition of two new formats: the compact 384 x 288 for low SWaP applications, and the large 1024 x 768 format for applications requiring high resolution and a wide field of view.Defence Science Journal, 2013, 63(6), pp.555-570, DOI:http://dx.doi.org/10.14429/dsj.63.575