| 1. |
- Andersson, J. Y., et al.
(author)
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Quantum structure based infrared detector research and development within Acreo's centre of excellence IMAGIC
- 2010
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In: Infrared physics & technology. - : Elsevier BV. - 1350-4495 .- 1879-0275. ; 53:4, s. 227-230
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Journal article (peer-reviewed)abstract
- Acreo has a long tradition of working with quantum structure based infrared (IR) detectors and arrays. This includes QWIP (quantum well infrared photodetector), QDIP (quantum dot infrared photodetector), and InAs/GaInSb based photon detectors of different structure and composition. It also covers R&D on uncooled microbolometers. The integrated thermistor material of such detectors is advantageously based on quantum structures that are optimised for high temperature coefficient and low noise. Especially the SiGe material system is preferred due to the compatibility with silicon technology. The R&D work on IR detectors is a prominent part of Acreo's centre of excellence "IMAGIC" on imaging detectors and systems for non-visible wavelengths. IMAGIC is a collaboration between Acreo, several industry partners and universities like the Royal Institute of Technology (KTH) and Linkoping University. (C) 2010 Elsevier B.V. All rights reserved.
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| 2. |
- Andersson, J. Y., et al.
(author)
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SiGe/Si quantum structures as a thermistor material for low cost IR microbolometer focal plane arrays
- 2011
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In: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 60:1, s. 100-104
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Journal article (peer-reviewed)abstract
- Uncooled microbolometer thermal infrared detector technology is presently revolutionizing the infrared technology field. Essential improvement of the cost/performance ratio would be achieved by microbolometer arrays with higher sensitivity, since this allows the use of simpler and less costly camera optics, which implies a lower cost of the complete IR camera. The sensitivity of the microbolometers depends critically on the signal-to-noise ratio of the integrated thermistor material, which is set by its temperature coefficient of resistance (TCR) and noise characteristics. In this work we have investigated the use of epitaxial silicon-germanium/silicon (SiGe/Si) quantum well (QW) structures as a thermistor material. Si0.68Ge0.32/Si QW structures typically give a TCR of 3.0%/K and low noise values. A calculation of the noise equivalent temperature NETD of a bolometer gives 25 mK using the following assumptions: f-number = 1, 30 Hz video frame rate for a 640 x 480 array, with a pixel size 25 x 25 mu m. Higher TCR values are foreseen for SiGe/Si quantum dot structures, and the noise is expected to be similar to the QW based structures.
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| 3. |
- Ericsson, Per, et al.
(author)
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Toward 17µm pitch heterogeneously integrated Si/SiGe quantum well bolometer focal plane arrays
- 2011
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In: Infrared Technology and Applications XXXVII. - : SPIE - International Society for Optical Engineering. ; , s. 801216-1-801216-9
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Conference paper (peer-reviewed)abstract
- Most of today's commercial solutions for un-cooled IR imaging sensors are based on resistive bolometers using either Vanadium oxide (VOx) or amorphous Silicon (a-Si) as the thermistor material. Despite the long history for both concepts, market penetration outside high-end applications is still limited. By allowing actors in adjacent fields, such as those from the MEMS industry, to enter the market, this situation could change. This requires, however, that technologies fitting their tools and processes are developed. Heterogeneous integration of Si/SiGe quantum well bolometers on standard CMOS read out circuits is one approach that could easily be adopted by the MEMS industry. Due to its mono crystalline nature, the Si/SiGe thermistor material has excellent noise properties that result in a state-ofthe- art signal-to-noise ratio. The material is also stable at temperatures well above 450°C which offers great flexibility for both sensor integration and novel vacuum packaging concepts. We have previously reported on heterogeneous integration of Si/SiGe quantum well bolometers with pitches of 40μm x 40μm and 25μm x 25μm. The technology scales well to smaller pixel pitches and in this paper, we will report on our work on developing heterogeneous integration for Si/SiGe QW bolometers with a pixel pitch of 17μm x 17μm.
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| 4. |
- Forsberg, Fredrik, et al.
(author)
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High-performance quantum-well silicon-germanium bolometers using IC-compatible integration for low-cost infrared imagers
- 2009
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In: TRANSDUCERS 2009. ; , s. 2214-2217
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Conference paper (peer-reviewed)abstract
- This paper reports on the realization and characterization of the very first quantum-well (QW) mono-crystalline Si/SiGe 18x18 pixel infrared bolometer arrays that are manufactured using IC compatible heterogeneous 3D integration on fan-out wafers. This integration process enables bolometer materials on top of CMOS-based integrated circuits that can not be integrated with conventional monolithic deposition techniques. The manufactured bolometer arrays have a negative temperature coefficient of resistance (TCR) of 2.8%/K. Measurements of the 1/f noise showed a higher value than expected for the bolometers. This result can be compared to lower values of noise achieved for samples of the thermistor material and is believed to result from imperfect metal contacts.
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| 5. |
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| 6. |
- Kvisteroy, Terje, et al.
(author)
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Far infrared low-cost uncooled bolometer for automotive use
- 2007
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In: Advanced Microsystems for Automotive Applications 2007. - BERLIN : SPRINGER-VERLAG BERLIN. - 9783540713241 ; , s. 265-278
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Conference paper (peer-reviewed)abstract
- A proposed EU regulation requires the automotive industry to develop technologies that will substantially decrease the risk for vulnerable road users such as pedestrians when hit by a vehicle. Automatic brake assist systems, activated by a suitable sensor, will reduce the speed of the vehicle before the impact. Far InfraRed (FIR) detectors are ideal candidates for such sensing systems. In order to enable high volume serial installation, the main development must be focused on cost reduction. Optimizing all aspects of the system, including sensor size, production yield and 3D wafer level vacuum packaging will lower today's "high end" FIR product costs by an order of magnitude. A low-cost FIR infrared bolometer is developed in the Eureka labeled PIMS (Pedestrian Injury Mitigation System) project. In the paper the background and the actual design of the first demonstrator to be finished in 2008 are described in detail.
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| 7. |
- Radamson, Henry H., et al.
(author)
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Carbon-doped single-crystalline SiGe/Si thermistor with high temperature coefficient of resistance and low noise level.
- 2010
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:22, s. 223507-
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Journal article (peer-reviewed)abstract
- SiGe (C)/Si(C) multiquantum wells have been studied as a thermistor material for future bolometers. A thermistor material for uncooled Si-based thermal detectors with thermal coefficient of resistance of 4.5%/K for 100 x 100 mu m(2) pixel sizes and low noise constant (K-1/f) value of 4.4 x 10(-15) is presented. The outstanding performance of the devices is due to Ni-silicide contacts, smooth interfaces, and high quality multiquantum wells containing high Ge content.
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| 8. |
- Roxhed, Niclas, et al.
(author)
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Low-cost uncooled microbolometers for thermal imaging
- 2010
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In: OPTICAL SENSING AND DETECTION. - : SPIE. - 9780819481993 ; , s. 772611-
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Conference paper (peer-reviewed)abstract
- Cost efficient integration technologies and materials for manufacturing of uncooled infrared bolometer focal plane arrays (FPA) are presented. The technology platform enables 320x240 pixel resolution with a pitch down to 20 mu m and very low NETD. A heterogeneous 3D MEMS integration technology called SOIC (Silicon-On-Integrated-Circuit) is used to combine high performance Si/SiGe bolometers with state-of-the-art electronic read-out-integrated-circuits. The SOIC integration process consists of: (a) Separate fabrication of the CMOS wafer and the MEMS wafer. (b) Adhesive wafer bonding. (c) Sacrificial removal of the MEMS handle wafer. (d) Via-hole etching. (e) Via formation and MEMS device definition. (f) Sacrificial etching of the polymer adhesive. We will present an optimized process flow that only contains dry etch processes for the critical process steps. Thus, extremely small, sub-micrometer feature sizes and vias can be implemented for the infrared bolometer arrays. The Si/SiGe thermistor is grown epitaxially, forming a mono-crystalline multi layer structure. The temperature coefficient of resistance (TCR) is primarily controlled by the concentration of Ge present in the strained SiGe layers. TCR values of more than 3%/K can be achieved with a low signal-to-noise ratio due to the mono-crystalline nature of the material. In addition to its excellent electrical properties, the thermistor material is thermally stable up to temperatures above 600 degrees C, thus enabling the novel integration and packaging techniques described in this paper. Vacuum sealing at the wafer level reduces the overall costs compared to encapsulation after die singulation. Wafer bonding is performed using a Cu-Sn based metallic bonding process followed by getter activation at >= 350 degrees C achieving a pressure in the 0.001 mbar range. After assembling, the final metal phases are stable and fully compatible with high-temperature processes. Hermeticity over the product lifetime is accomplished by well-controlled electro-deposition of metal layers, optimized bonding parameters and a suitable bond frame design.
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| 9. |
- Vieider, Christian, et al.
(author)
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Low-cost far infrared bolometer camera for automotive use
- 2007
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In: P SOC PHOTO-OPT INSTRUM ENG. - : SPIE. - 9780819466648 ; , s. 5421-5421
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Conference paper (peer-reviewed)abstract
- A new low-cost long-wavelength infrared bolometer camera system is under development. It is designed for use with an automatic vision algorithm system as a sensor to detect vulnerable road users in traffic. Looking 15 in in front of the vehicle it can in case of an unavoidable impact activate a brake assist system or other deployable protection system. To achieve our cost target below epsilon 100 for the sensor system we evaluate the required performance and can reduce the sensitivity to 150 mK and pixel resolution to 80 x 30. We address all the main cost drivers as sensor size and production yield along with vacuum packaging, optical components and large volume manufacturing technologies. The detector array is based on a new type of high performance thermistor material. Very thin Si/SiGe single crystal multi-layers are grown epitaxially. Due to the resulting valence barriers a high temperature coefficient of resistance is achieved (3.3%/K). Simultaneously, the high quality crystalline material provides very low 1/f-noise characteristics and uniform material properties. The thermistor material is transferred from the original substrate wafer to the read-out circuit using adhesive wafer bonding and subsequent thinning. Bolometer arrays can then be fabricated using industry standard MEMS process and materials. The inherently good detector performance allows us to reduce the vacuum requirement and we can implement wafer level vacuum packaging technology used in established automotive sensor fabrication. The optical design is reduced to a single lens camera. We develop a low cost molding process using a novel chalcogenide glass (GASIR (R) 3) and integrate anti-reflective and anti-erosion properties using diamond like carbon coating.
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| 10. |
- Wissmar, Stanley, et al.
(author)
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SiGe quantum wells for uncooled long wavelength infra-red radiation (LWIR) sensors
- 2008
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In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY. - : IOP Publishing.
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Conference paper (peer-reviewed)abstract
- - We demonstrate a novel single-crystalline high-performance thermistor material based on SiGe quantum well heterostructures. The SiGe/Si quantum wells are grown epitaxially on standard Si [001] substrates. Holes are used as charge carriers utilizing the discontinuities in the valence band structure. By optimizing design parameters such as the barrier height (by variation of the germanium content) and the fermi level Ef (by variation of the quantum well width and doping level) of the material, the layer structure can be tailored. Then a very high temperature coefficient of resistivity (TCR) can be obtained which is superior to the previous reported conventional thin film materials such as vanadium oxide and amorphous silicon. In addition, the high quality crystalline material promises very low 1/f-noise characteristics promoting an outstanding signal to noise ratio as well as well defined and uniform material properties. High-resolution X-ray diffraction was applied to characterize the thickness and Ge content of QWs. The results show sharp oscillations indicating an almost ideal super lattice with negligible relaxation and low defect density. The impact of growth temperature on the thermistor material properties was characterized by analyzing how the resulting strain primarily affects the performance of the TCR and 1/f noise. Results illustrate a value of 3.3 %/K for TCR with a low 1/f noise.
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