Uncooled IR Sensors Research Articles

On the Role of Thermal Imaging in Automotive Applications: A Critical Review

For decades, the number of automobiles in urban areas around the world has been increasing. It causes serious challenges such as traffic congestion, accidents, and pollution, which have a social, economic, and environmental impact on widespread urban cities. To overcome these challenges, we need to explore smart AI-based perception systems for vehicular applications. Such types of systems can provide improved situational awareness to the driver and generate early alarm about upcoming obstacles and road incidents. In this study, we have presented the effective use of uncooled thermal IR sensors for designing smart thermal perception systems as an alternative to CMOS visible imaging by presenting state-of-the-art studies for in-cabin and out-cabin vehicular applications with potential long-term benefits for the automotive industry. The key rationale for selecting thermal IR sensors over conventional image sensors is that visible cameras are highly dependent on lighting conditions and performance is degraded significantly in low-lighting scenarios and harsh weather conditions. Contrary to this, thermal sensors remain largely unaffected by external lighting conditions or most environmental conditions, making it a perfect optical sensor choice for all-weather and harsh environmental conditions. This study presents a review of the current state of the art for automotive thermal imaging with a focus on the contributions and advances achieved by the EU-funded project ‘HELIAUS’ in the domain of AI-based thermal imaging pipelines for safer and reliable road journeys.

Comparison of Cooled and Uncooled IR Sensors by Means of Signal-to-Noise Ratio for NDT Diagnostics of Aerospace Grade Composites.

This work aims to address the effectiveness and challenges of non-destructive testing (NDT) by active infrared thermography (IRT) for the inspection of aerospace-grade composite samples and seeks to compare uncooled and cooled thermal cameras using the signal-to-noise ratio (SNR) as a performance parameter. It focuses on locating impact damages and optimising the results using several signal processing techniques. The work successfully compares both types of cameras using seven different SNR definitions, to understand if a lower-resolution uncooled IR camera can achieve an acceptable NDT standard. Due to most uncooled cameras being small, lightweight, and cheap, they are more accessible to use on an unmanned aerial vehicle (UAV). The concept of using a UAV for NDT on a composite wing is explored, and the UAV is also tracked using a localisation system to observe the exact movement in millimetres and how it affects the thermal data. It was observed that an NDT UAV can access difficult areas and, therefore, can be suggested for significant reduction of time and cost.

Modeling the Performance of Mosaic Uncooled Passive IR Sensors in CMOS–SOI Technology

This paper analyzes the performance of mosaic nonimaging passive infrared (PIR) sensors fabricated by the CMOS–SOI–MEMS technology. The elementary sensor, forming a subpixel, is a thermally isolated nanomachined CMOS transistor, dubbed TMOS, operating at subthreshold. The mosaic uncooled PIR sensors are composed of several TMOS subpixels, which are electrically connected, either in parallel or in series as well as a combination of both options. These mosaic sensors, which are manufactured by nanofabrication methods, exhibit enhanced performance and robust manufacturing on wafer level. The overall figures of merit of these sensors, which are modeled in this paper, indicate why they are most suitable for consumer electronics, including smart homes, wearables, Internet of Things as well as mobile applications.

Modeling the Performance of Nano Machined CMOS Transistors for Uncooled IR Sensing

This paper models the performance and summarizes the design considerations (electrical, mechanical, and thermal) of CMOS-SOI-NEMS (CMOS Silicon on Insulator nanoelectro mechanical systems) transistors fabricated in the 130-nm technology, which perform as uncooled passive infrared (PIR) sensors. The nanmachined CMOS-SOI-NEMS transistors (dubbed TMOS) are isolated thermally by the postprocessing dry etching with high yield and uniformity, achieved at the wafer-level processing as well as the wafer-level packaging, using 8-in wafers. The TMOS transistor is an active sensor with internal gain achieving voltage, responsivity, over $10^{7}$ V/W. This responsivity is larger by approximately an order of magnitude compared to bolometers, and several orders of magnitude compared to thermopiles or pyros, which are passive devices. The TMOS operates at subthreshold, requiring very low power, of the order of microWatt. Accordingly, this uncooled IR sensor, in the low-cost CMOS-SOI technology, promises to become the standard PIR technology for mobile applications, wearables, and Internet of Things.

The development of a μ-biomimetic uncooled IR-Sensor inspired by the infrared receptors of Melanophila acuminata

The beetle Melanophila acuminata uses a specialized organ to detect infrared radiation. The organ consists of about 100 individual sensilla. The main component of the sensillum is a pressure chamber. Upon absorption of radiation, the pressure increases, and the tip of a dendrite is deformed. A unique feature of the organ is a compensation mechanism that prevents large pressures. The beetle uses this organ to detect forest fires and to navigate inside burning woods. However, the sensitivity is part of a long-lasting discussion, providing thresholds between and . To end the decade-long discussion and to provide a novel type of infrared sensor, we are developing an uncooled μ-biomimetic infrared (IR) sensor inspired by Melanophila acuminata using MEMS technology. Here, we present the development of a μ-capacitor that is used to detect pressure changes and the characterization of the compensation mechanism. We describe the microtechnological fabrication process for air-filled capacitors with a ratio of diameter-to-electrode distance of 1000 and a technique to fill the sensor bubble-free with water. Finally, we estimate the sensitivity of the beetle using a theoretical model of the sensillum.

Control of Metal-Insulator Transition of Vanadium Dioxide Thin Film Grown by Excimer Laser Assisted Metal Organic Deposition

In order to fabricate the new devices for the next generation, it is necessary to develop new materials, nanostructured thin films, low temperature processing. To achieve these aims, we have developed the photo-induced chemical solution deposition such as excimer laser-assisted metal organic deposition (ELAMOD) and photo reaction of nano-particle method (PRNP) for the preparation of the patterned metal oxide thin film on organic, glass and single crystalline substrates. In this presentation, we will talk about epitaxial VO2 thin film with nanostructure by using the photo-induced chemical solution deposition, and its excellent properties of the thin film for new uncooled IR sensor.

Fabrication of Monolithic Integrated Bimaterial Resonant Uncooled IR Sensor

In this work we studied the fabrication of a monolithic bimaterial micro-cantilever resonant IR sensor with on-chip drive circuits. The effects of high temperature process and stress induced performance degradation were investigated. The post-CMOS MEMS (micro electro mechanical system) fabrication process of this IR sensor is the focus of this paper, starting from theoretical analysis and simulation, and then moving to experimental verification. The capacitive cantilever structure was fabricated by surface micromachining method, and drive circuits were prepared by standard CMOS process. While the stress introduced by MEMS films, such as the tensile silicon nitride which works as a contact etch stopper layer for MOSFETs and releasing stop layer for the MEMS structure, increases the electron mobility of NMOS, PMOS hole mobility decreases. Moreover, the NMOS threshold voltage (Vth) shifts, and transconductance (Gm) degrades. An additional step of selective removing silicon nitride capping layer and polysilicon layer upon IC area were inserted into the standard CMOS process to lower the stress in MOSFET channel regions. Selective removing silicon nitride and polysilicon before annealing can void 77% Vth shift and 86% Gm loss.

Modelling a Historic Oil-Tank Fire Allows an Estimation of the Sensitivity of the Infrared Receptors in Pyrophilous Melanophila Beetles

Pyrophilous jewel beetles of the genus Melanophila approach forest fires and there is considerable evidence that these beetles can detect fires from great distances of more than 60 km. Because Melanophila beetles are equipped with infrared receptors and are also attracted by hot surfaces it can be concluded that these infrared receptors are used for fire detection.The sensitivity of the IR receptors is still unknown. The lowest threshold published so far is 0.6 W/m2 which, however, cannot explain the detection of forest fires by IR radiation from distances larger than approximately 10 km. To investigate the possible sensitivity of the IR receptors we assumed that beetles use IR radiation for remote fire detection and we made use of a historic report about a big oil-tank fire in Coalinga, California, in 1924. IR emission of an oil-tank fire can be calculated by “pool fire” simulations which now are used for fire safety and risk analysis. Assuming that beetles were lured to the fire from the nearest forests 25 and 130 km away, our results show that detection from a distance of 25 km requires a threshold of the IR receptors of at least 3×10−2 W/m2. According to our investigations most beetles became aware of the fire from a distance of 130 km. In this case the threshold has to be 1.3×10−4 W/m2. Because such low IR intensities are buried in thermal noise we suggest that the infrared sensory system of Melanophila beetles utilizes stochastic resonance for the detection of weak IR radiation. Our simulations also suggest that the biological IR receptors might be even more sensitive than uncooled technical IR sensors. Thus a closer look into the mode of operation of the Melanophila IR receptors seems promising for the development of novel IR sensors.

Uncooled infrared sensor technology for hostile fire indication systems

An evolving combat arena poses an ever-growing hostile fire threat for various ground and airborne targets. Protecting both static posts and moving military platforms against these threats require high performance and affordable solutions, favoring uncooled sensing alert technologies. By analyzing accumulated target and clutter data using new algorithmic and hardware building blocks we establish improved hostile fire indication system configurations. The paper will review new system demonstrations harnessing uncooled IR sensors technology alongside empirical field testing results.

Trilayered Ceramic–Metal–Polymer Microcantilevers with Dramatically Enhanced Thermal Sensitivity

Trilayered ceramic–metal–polymer thermally sensitive microcantilevers with the topmost polymer nanocomposite layers reinforced with carbon nanotubes and metal nanoparticles are described (see figure and inside cover). These trilayered microcantilevers show dramatically enhanced thermal sensitivity and could be used in next-generation uncooled IR sensor arrays with thermal and spatial resolution many times higher than currently available sensors.

Fabrication and characterization of integrated uncooled infrared sensor arrays using a-Si thin-film transistors as active elements

In this paper, we report on the first realization and characterization of monolithic uncooled 8/spl times/8 infrared sensor arrays, based on amorphous silicon thin-film transistors (a-Si TFT). The a-Si TFT is employed as the active element of the sensor, because it possesses a high temperature coefficient of its drain current of 1.5%-6.5% K/sup -1/ at room temperature. The improved porous silicon micromachining techniques described here enable the integration of the a-Si TFT-based sensor array with the MOS readout circuitry. The sacrificial material of porous silicon is prepared in the first step. It is then well protected all the time during the fabrication of MOSFETs and sensors before being released. Optical tests are performed to characterize the sensor. The influences of the gate voltage of a-Si TFT (V/sub g/) and the voltage source of the circuitry (V/sub dd/) on the sensor performance are investigated. The measurement indicates that the sensor has a maximum detectivity of 8.67/spl times/10/sup 8/ cm Hz/sup 1/2/W/sup -1/ at V/sub g/=-15 V, V/sub dd/=-12 V and a chopping frequency of 30 Hz. The noise equivalent power (NEP) of the sensor is less than 10/sup -10/ W Hz/sup -1/2/, and the noise equivalent temperature difference (NETD) is as low as 67 mK at room temperature, which compares well with the recent results of some uncooled IR sensors developed by other groups. Primary imaging tests indicate that the 8/spl times/8 sensor array has potential for high performance imaging applications.

Complete analytical modeling and analysis of micromachined thermoelectric uncooled IR sensors

This paper deals with a complete analytical modeling and analysis of thermoelectric uncooled infrared sensors compatible with CMOS technology. The operating principle involves a localized thermal assessment resulting from IR radiation absorption, a micromachined membrane on which PolySi/Al thermojunctions have been deposited causing an internal self-generated electromotive force. The model put forward is based on dividing the sensor into three zones, each one being the subject of a thorough thermal study (conduction, convection and radiation thermal effect). Through the analytical thermal gradient analysis developed in each zone of the structure (absorber, part of thermoelectric transducer layer placed under the absorber, thermoelectric transducer) we are able to predict the sensitivity, detectivity and the noise equivalent power to the sensor. Thus, such a kind of analytical approach is worth of interest to optimize thermopile sensor design parameters.

Influences of thin Ni layer on the electrical and absorption properties of PZT thin film pyroelectric IR sensors

A solid precursor was used to prepare ferroelectric lead zirconate titanate (PZT) 30/70 thin films using the sol–gel deposition method. To apply PZT thin films for uncooled pyroelectric IR sensors, a Ni layer was deposited onto the PZT thin films, serving both as a selective absorption layer and as the top electrode. The absorption properties of such Ni coated multi-layered pyroelectric sensors were studied in the visible and infrared wavelength ranges. The maximum absorption coefficient of this type of IR sensor was measured to be 0.8 at 0.633 μm and 0.7 at 4 μm wavelength, respectively. A striking asymmetric polarization hysteresis loop in these PZT thin films with Ni as the top electrode was observed as a direct consequence. This asymmetric polarization was attributed to cause the difference in the dynamic pyroelectric responses in these Ni/PZT/Pt films, poled either positively or negatively before the measurement.

Multi-element uncooled sensors based on organic pyroelectric films integrated with CCD

We present some new experimental results on physical properties and time behavior of polycyclic organic compound (TADPh) and polyvinylidene fluoride (PVDF) pyroelectric films for uncooled IR array sensors. The thin films fabrication technologies were optimized as regard to the best figure of merit and to compatibility with CMOS technology. We developed the fabrication process of uncooled pyroelectric IR sensors with photosensitive elements isolated from the substrate by an air gap. The IR sensor arrays containing 2×128 sensitive elements and special low-noise bulk-channel CCDs were fabricated for the sake of experiments.

A heat transfer analysis for quartz microresonator IR sensors

To aid the design of uncooled IR sensors based on quartz microresonators, a heat transfer analysis is carried out for the time-dependent temperature distribution in the resonator. The quartz resonator is taken to be circular, homogeneous isotropic, with a ring electrode on its front surface which is IR illuminated. It is assumed that the microresonator array is packaged in high vacuum; the side and back surfaces of the resonator are thermally insulated. Only heat conduction within the quartz resonator is considered; radiation at the surfaces and heat conduction through the bridges that link the resonator to the base structure are neglected. The boundary value problem of heat conduction in the resonator is solved analytically; expressions for the temperature distribution before and after the photon flux is turned off are given. It is found that for the quartz resonator under study, the time is required to reach a uniform temperature distribution in the entire resonator (the time constant) is critically dependent on the photon absorptivity of the ring electrode on the front surface. For example, when the ring electrode has no effect on photon absorption, t8 = 9.52 microseconds; however, if the ring electrode is fully reflective, t8 = 4.76 milliseconds. These time constants are expected to play an important role in the design of the quartz microresonator IR sensors.

An uncooled IR sensor with digital focal plane array.

This article reports on state-of-the-art improvements in microbolometer technology through an ongoing set of laboratory and field experiments. The availability of low-cost, high thermal and physical resolution digital IR imaging equipment may provide a new method for the investigation of human circulatory conditions, resulting in improved diagnostic and therapeutic approaches to a wide variety of medical applications.