Search

Uncooled infrared focal plane arrays (IR FPAs) have seen unprecedented growth over the last decade and ubiquitously extending its application beyond the military realm into various diverse areas such as: surveillance, security and law enforcement, thermography (predictive maintenance, building inspection), industrial process control, automotive safety and medical imaging. The uncooled microbolometers are mainly used for imaging in long wave infrared spectral range (LWIR). In the recent years, the e orts made for the technical evolution of the microbolometer involves: pixel size reduction, new materials and designs to enhance the detection and integration capability. Currently, Vanadium oxide VOx together with a-Si based FPAs have the major share in the uncooled imaging market. Nevertheless, they o er limited performance in terms of the thermal sensitivity. Here we present, an epitaxially grown Si/Si1-xGex multi-quantum-well (MQW) detector as a potential candidate to improve the thermal sensitivity due to its inherent fringe bene t of ease of the bandgap tailoring by increasing the Ge content up to 50 %. It offers low flicker noise attributed to its single crystalline properties. The predictive technology computer-aided design (TCAD) tool has been used to obtain a priori estimate to design and develop Si/Si1-xGex MQW detector. A comprehensive predictive device model is developed to investigate the electrical characteristics of Si/Si1-xGex MQW, device design challenges and design trade-o s. The integrated self-consistent numerical modeling framework incorporates the number of interdependent design variables such as Ge content, active device areas, the doping pro les, the thickness and the periodicity of quantum wells. The model is employed to optimize Ge content and the doping pro le for the desired Figure-of merits specified in terms of the temperature coefficient of resistance (TCR) and dc resistance (R). The modeling results are validated with the experimental data and found consistent over a wide range of Ge content varied from 30% up to 50 %. The model predicts TCR can be raised up to 5.4%K-1 by incorporating 50% Ge content in MQW (experimentally verified) where the measured flicker noise constant k1=f of the detector is 5.8 10-13.

This paper presents a partially pixel-parallel digital readout integrated circuit (DROIC) that overcomes the limitation of achievable digital resolution seen in megapixel-format infrared digital focal plane arrays (IR-DFPAs). It incorporates 5-bit inpixel pulse frequency modulation (PFM) based charge-todigital converters and 10-bit successive approximation register (SAR) column analog to digital converters (ADCs). To increase the readout resolution, the residue charge at the end of the integration phase is fine converted to a 10-bit digital word and combined with the in-pixel data. This method is a compromise between fully pixelparallel and fully column-parallel conversion approaches and favors the ever-growing trend towards small pitch FPAs by allowing a compact pixel size. A prototype consisting of a 32×32 array of pixels, 32 column SAR ADCs and a timing controller block is designed and fabricated in a 90nm bulk CMOS process. A modified version of the conventional PFM based pixel is designed to help hold the residue charge. The design is targeted at mediumwave IR-DFPAs with frame rates up to 400 Hz. An SNR of 79 dB is achieved with a full-well capacity of 2.4 Me-.

Uzun dalga kızılötesi frekans bandına duyarlı soğutmasız kızılötesi görüntüleme sistemleri pazarı son yıllarda büyük bir büyüme göstermiştir ve kullanım alanları askeri uygulamalardan farklı alanlara kaymaya başlamıştır: gözetleme, güvenlik, termal görüntüleme (öngörülebilir onarım, bina muayenesi), endüstriyel üretim kontrolü, otomotiv güvenliği ve medikal görüntüleme. Son yıllarda bolometrelerin iyileştirilmesi için yapılan çalışmalar şu noktalarda yoğunlaşmıştır: piksel boyutunun küçültülmesi, yeni malzemeler ve tasarım teknikleriyle algılama ve entegrasyon kabiliyetlerinin geliştirilmesi. Halihazırda bolometre pazarında en çok kullanılan malzemeler Vanadyum Oksit (VOx) ve amorf silikon (a-Si) malzemeleridir. Fakat bu malzemeler termal hassaslık bakımından yeterli performans sunamamaktadır. Bu tezde epitaksiyel olarak büyütülmüş Si/Si1-xGex çoklu-kuantum kuyulu malzeme yapısı bolometrelerin termal algıla hassaslığının geliştirilmesi için önerilmiştir. Bu yapıda Ge içeriğini %50'ye kadar artırarak yarıiletken bant aralığını değiştirmek ve tekli kristal yapısı dolayısıyla düşük kırpışma gürültüsü elde etmek mümkün olmaktadır. Si/Si1-xGex çoklu-kuantum kuyu bolometreyi modellemek, tasarlamak ve geliştirmek için TCAD yarıiletken yazılımı kullanılmıştır. Si/Si1-xGex çoklu kuantum kuyu bolometrenin elektriksel karakteristiklerinin çıkarılması, tasarım zorluklarının belirlenmesi ve tasarımda birbirlerini etkileyen parametrelerin optimizasyonunun yapılabilmesi icin kapsamlı bir model çıkarılmıştır. Geliştirilen model birbiriyle ilişkili Ge içeriği, aktif aygıt alanı, katkılama profilleri, katmanların kalınlıkları, kuantum kuyularının periyodisitesi gibi parametreleri içermektedir. Geliştirilen model kullanılarak istenilen TCR (sıcaklığa bağlı direnç değişim katsayısı) ve dc direnç değerlerine ulaşabilmek için Ge içeriğinin miktarı ve katkılama profilleri(katman kalınlıkları, katkılama oranı, vs) belirlenebilmektedir. Geliştirilen model %30 ile %50 aralığında değişen Ge içeriğine göre elde edilen TCR ve direnç değerleri ile deneysel olarak doğrulanmıştır. Geliştirilen model %50 Ge içerik ile %5.4K-1 TCR değerine ulaşabileceğini göstermiştir. Uncooled infrared focal plane arrays (IR FPAs) have seen unprecedented growth over the last decade and ubiquitously extending its application beyond the military realm into various diverse areas such as: surveillance, security and law enforcement, thermography (predictive maintenance, building inspection), industrial process control, automotive safety and medical imaging. The uncooled microbolometers are mainly used for imaging in long wave infrared spectral range (LWIR). In the recent years, the e orts made for the technical evolution of the microbolometer involves: pixel size reduction, new materials and designs to enhance the detection and integration capability. Currently, Vanadium oxide VOx together with a-Si based FPAs have the major share in the uncooled imaging market. Nevertheless, they o er limited performance in terms of the thermal sensitivity. Here we present, an epitaxially grown Si/Si1-xGex multi-quantum-well (MQW) detector as a potential candidate to improve the thermal sensitivity due to its inherent fringe bene t of ease of the bandgap tailoring by increasing the Ge content up to 50 %. It offers low flicker noise attributed to its single crystalline properties. The predictive technology computer-aided design (TCAD) tool has been used to obtain a priori estimate to design and develop Si/Si1-xGex MQW detector. A comprehensive predictive device model is developed to investigate the electrical characteristics of Si/Si1-xGex MQW, device design challenges and design trade-o s. The integrated self-consistent numerical modeling framework incorporates the number of interdependent design variables such as Ge content, active device areas, the doping pro les, the thickness and the periodicity of quantum wells. The model is employed to optimize Ge content and the doping pro le for the desired Figure-of merits specified in terms of the temperature coefficient of resistance (TCR) and dc resistance (R). The modeling results are validated with the experimental data and found consistent over a wide range of Ge content varied from 30% up to 50 %. The model predicts TCR can be raised up to 5.4%K-1 by incorporating 50% Ge content in MQW (experimentally verified) where the measured flicker noise constant k1=f of the detector is 5.8 10-13. 126

Digital pixels based on pulse frequency modulation (PFM) employ counting techniques to achieve very high charge handling capability compared to their analog counterparts. Moreover, extended counting methods making use of left-over charge (residue) on the integration capacitor help improve the noise performance of these pixels. However, focal plane arrays (FPAs) with small pixel pitch are constrained in terms of pixel area, which makes it difficult to benefit from in-pixel extended counting circuitry. Thus, in this paper, the authors propose a novel approach to measure the residue outside the pixel using an analog-to-digital converter (ADC). A first prototype of the proposed pixel, in the form of a testbed, has been developed which is aimed at medium-wave infrared (MWIR) imaging arrays having small pixel pitch. The prototype is composed of a pixel front end, a 12-bit SAR ADC, a counter, and a comparator. The front-end is a modified version of the conventional design and has been designed and fabricated in 90nm CMOS, whereas off-the-shelf discrete components have been used to implement the ADC, comparator, and counter. Measured signal-to-noise ratio (SNR) at low illumination levels is 55dB.