Thermal and flicker noise improvement in short-channel CMOS detectors

Integrated circuit (IC) technology has emerged as a suitable platform for infrared (IR) detector development. This technology is however susceptible to on-chip intrinsic noise. By using double-gate MOSFETs for detectors in the near-IR band, noise performance in the readout circuitry is improved, thereby enhancing the overall performance of these detectors. A 1 dB reduction in low-frequency noise is achieved, which is verified through simulations. It is shown that by using short-channel devices that noise improvement is furthermore obtained due to reduction in threshold voltage variation. The double-gate concept is applied in simulation to the three-transistor pixel topology and can also be implemented in other detector topologies such as the four-transistor pixel topology, since readout noise is not limited to specific IR detector topologies. The overall performance of near-IR detectors and the fill factor are significantly improved. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Dynamic range and sensitivity improvement in near-infrared detectors using silicon germanium bipolar complementary metal-oxide semiconductor technology

Classically gated infrared (IR) detectors have been implemented using charge-coupled devices (CCD). Bipolar complementary metal-oxide semiconductor (BiCMOS) technology emerged as a viable alternative platform for development. BiCMOS technology has a number of advantages over CCD and conventional CMOS technology, of which increased switching speed is one. The pixel topology used in this work is a reversed-biased diode connected heterojunction bipolar transistor. The disadvantage of CMOS detectors is the increased readout noise due to the increased on-chip switching compared to CCD, which degrades dynamic range (DR) and sensitivity. This yields increased switching speeds compared to conventional bipolar junction transistors. Sensitivity improved from 50 mA∕W (peak) at 430 nm in CCD detectors to 180 mA∕W (peak) (or 180; 000 V∕W) at 665 nm in BiCMOS detectors. Other CMOS IR detectors previously published in the literature showed sensitivity values from 2750 to 5000 V∕W or 100 mA∕W. The DR also improved from 47 and 53 dB to 70 dB. The sensitivity of conventional CCD detectors previously published is around 53 mA∕W. The second advantage is that detection in the near-IR band with conventional silicon integrated technology is possible. This work has shown increased detection capabilities up to 1.1 μm compared to Si detectors.The authors would like to thank Armscor, the Armament Corporation of South Africa Ltd (Act 51 of 2003) for financial assistance. The administration of the grant was facilitated through the Defence, Peace, Safety, and Security (DPSS) business unit of the Council for Scientific and Industrial Research (CSIR), South Africa.http://spie.org/x867.xmlam201

Dynamic range and sensitivity improvement of infrared detectors using BiCMOS technology

The field of infrared (IR) detector technology has shown vast improvements in terms of speed and performance over the years. Specifically the dynamic range (DR) and sensitivity of detectors showed significant improvements. The most commonly used technique of implementing these IR detectors is the use of charge-coupled devices (CCD). Recent developments show that the newly investigated bipolar complementary metal-oxide semiconductor (BiCMOS) devices in the field of detector technology are capable of producing similar quality detectors at a fraction of the cost. Prototyping is usually performed on low-cost silicon wafers. The band gap energy of silicon is 1.17 eV, which is too large for an electron to be released when radiation is received in the IR band. This means that silicon is not a viable material for detection in the IR band. Germanium exhibits a band gap energy of 0.66 eV, which makes it a better material for IR detection. This research is aimed at improving DR and sensitivity in IR detectors. CCD technology has shown that it exhibits good DR and sensitivity in the IR band. CMOS technology exhibits a reduction in prototyping cost which, together with electronic design automation software, makes this an avenue for IR detector prototyping. The focus of this research is firstly on understanding the theory behind the functionality and performance of IR detectors. Secondly, associated with this, is determining whether the performance of IR detectors can be improved by using silicon germanium (SiGe) BiCMOS technology instead of the CCD technology most commonly used. The Simulation Program with Integrated Circuit Emphasis (SPICE) was used to realise the IR detector in software. Four detectors were designed and prototyped using the 0.35 µm SiGe BiCMOS technology from ams AG as part of the experimental verification of the formulated hypothesis. Two different pixel structures were used in the four detectors, which is the silicon-only p-i-n diodes commonly found in literature and diode-connected SiGe heterojunction bipolar transistors (HBTs). These two categories can be subdivided into two more categories, which are the single-pixel-single-amplifier detectors and the multiple-pixel-single-amplifier detector. These were needed to assess the noise performance of different topologies. Noise influences both the DR and sensitivity of the detector. The results show a unique shift of the detecting band typically seen for silicon detectors to the IR band, accomplished by using the doping feature of HBTs using germanium. The shift in detecting band is from a peak of 250 nm to 665 nm. The detector still accumulates radiation in the visible band, but a significant portion of the near-IR band is also detected. This can be attributed to the reduced band gap energy that silicon with doped germanium exhibits. This, however, is not the optimum structure for IR detection. Future work that can be done based on this work is that the pixel structure can be optimised to move the detecting band even more into the IR region, and not just partially.Dissertation (MEng)--University of Pretoria, 2013.Electrical, Electronic and Computer Engineeringunrestricte

Mathematical Modelling of Low-Frequency BiCMOS Near-Infrared Detector

Bipolar complementary metal-oxide semiconductor (BiCMOS) technology is the platform of choice for near-Infrared (IR) detector research because of low power consumption, increased operating speed and a high fill-factor. The drawback is poor noise performance which can be attributed to the readout circuitry of the detector. Conventional near-IR detector design is an iterative process. While recognising the value of this approach, rapid prototyping can be achieved by using mathematical modelling that would ensure design repeatability. Heterojunction bipolar transistor (HBT) and metal-oxide field-effect transistors (MOSFET) models for SiGe process technologies have been documented extensively. However, mathematical modelling of BiCMOS near-IR detectors has not been implemented in a complete working system before. This proposed model can be used to determine the output voltage as well as the noise performance of near-IR detectors. The focus of this research is to determine how process independent parameters and detector performance can be mathematically modelled. Secondly, and associated to this, is determining how the model can be extended to accommodate multiple feature sizes including short-channel MOSFETs. An implementation of this model on the three-transistor pixel structure, using reverse-biased diode-connected HBTs as pixels, was done as part of the experimental verification process of this research. The implementation was done in a 2 × 2 gated array detector configuration. The validity of the proposed modelling procedure was verified through comparison of simulations and measured results. The simulations were done in an iterative fashion to show how a deviation in one process independent parameter affects the noise performance, while the other process independent parameters are kept constant. The detector design with optimal noise performance can be achieved in this manner, thereby minimising design time and developing optimised detectors without the need for extensive prototyping. The main contribution of this research is that a designer can use this mathematical model to tune a detector to achieve desired performance. By changing the temperature, biasing voltage and biasing current and choosing the aspect ratio, noise performance changes. An iterative process in the mathematical model development can achieve optimised parameters for noise performance. Two approaches, namely DC analysis and y-parameter representation, were used to develop the mathematical model. Feedback was taken into account using the y-parameter representation. The measured results show that the output voltage behaviour follows the mathematical model developed. The output voltage behaviour also shows that the mathematical model parameters can determine noise performance. As an extension to this work, the same modelling process can be used to develop mathematical models for other detecting structures such as the four-transistor pixel structure.Thesis (PhD (Electronic Engineering))--University of Pretoria, 2020.Optronic Sensor Systems, Defence, Peace, Safety and Security (DPSS), Council for Scientific and Industrial Research (CSIR), South AfricaArmscor, Armaments Corporation of South Africa Limited Act, Act No 51 of 2003Department of International Relations, University of Pretoria, South AfricaNational Research Foundation (NRF), South AfricaElectrical, Electronic and Computer EngineeringPhD (Electronic Engineering)Unrestricte

Ultra-Low-Power Uwb Impulse Radio Design: Architecture, Circuits, And Applications

Recent advances in home healthcare, environmental sensing, and low power computing have created a need for wireless communication at very low power for low data rate applications. Due to higher energy/bit requirements at lower data -rate, achieving power levels low enough to enable long battery lifetime (~10 years) or power-harvesting supplies have not been possible with traditional approaches. Dutycycled radios have often been proposed in literature as a solution for such applications due to their ability to shut off the static power consumption at low data rates. While earlier radio nodes for such systems have been proposed based on a type of sleepwake scheduling, such implementations are still power hungry due to large synchronization uncertainty (~1[MICRO SIGN]s). In this dissertation, we utilize impulsive signaling and a pulse-coupled oscillator (PCO) based synchronization scheme to facilitate a globally synchronized wireless network. We have modeled this network over a widely varying parameter space and found that it is capable of reducing system cost as well as providing scalability in wireless sensor networks. Based on this scheme, we implemented an FCC compliant, 3-5GHz, timemultiplexed, dual-band UWB impulse radio transceiver, measured to consume only 20[MICRO SIGN]W when the nodes are synchronized for peer-peer communication. At the system level the design was measured to consume 86[MICRO SIGN]W of power, while facilitating multi- hop communication. Simple pulse-shaping circuitry ensures spectral efficiency, FCC compliance and ~30dB band-isolation. Similarly, the band-switchable, ~2ns turn-on receiver implements a non-coherent pulse detection scheme that facilitates low power consumption with -87dBm sensitivity at 100Kbps. Once synchronized the nodes exchange information while duty-cycling, and can use any type of high level network protocols utilized in packet based communication. For robust network performance, a localized synchronization detection scheme based on relative timing and statistics of the PCO firing and the timing pulses ("sync") is reported. No active hand-shaking is required for nodes to detect synchronization. A self-reinforcement scheme also helps maintain synchronization even in the presence of miss-detections. Finally we discuss unique ways to exploit properties of pulse coupled oscillator networks to realize novel low power event communication, prioritization, localization and immediate neighborhood validation for low power wireless sensor applications