This thesis describes the integration of temperature sensors into a CMOS image sensor (CIS). The temperature sensors provide the in-situ temperature of the pixels as well as the thermal distribution of the pixel array. The temperature and the thermal distribution are intended to be used to compensate for dark current affecting the CIS. Two different types of in-pixel temperature sensors have been explored. The first type of temperature sensor is based on a substrate parasitic bipolar junction transistor (BJT). The second type of temperature sensor that has been explored is based on the nMOS source follower (SF) transistor of the same pixel. The readout system that is used for the temperature sensors and for the image pixels is based on low noise column amplifiers. Both types of in-pixel temperature sensors (IPTS) have been designed implementing different techniques to improve their accuracy. The use of the IPTSs has been proved by measuring three prototypes chips. Also, a novel technique to compensate for the dark current of a CIS by using the IPTS has been proposed.@en

This article presents in-pixel (of a CMOS image sensor (CIS) temperature sensors with improved accuracy in the spatial and the temporal domain. The goal of the temperature sensors is to be used to compensate for dark (current) fixed pattern noise (FPN) during the exposure of the CIS. The temperature sensors are based on substrate parasitic bipolar junction transistor (BJT) and on the nMOS source follower of the pixel. The accuracy of these temperature sensors has been improved in the analog domain by using dynamic element matching (DEM), a temperature independent bias current based on a bandgap reference (BGR) with a temperature independent resistor, correlated double sampling (CDS), and a full BGR bias of the gain amplifier. The accuracy of the bipolar based temperature sensor has been improved to a level of ±0.25 °C, a 3σ variation of ±0.7 °C in the spatial domain, and a 3σ variation of ±1 °C in the temporal domain. In the case of the nMOS based temperature sensor, an accuracy of ±0.45 °C, 3σ variation of ±0.95 °C in the spatial domain, and ±1.4 °C in the temporal domain have been acquired. The temperature range is between-40 °C and 100 °C.

@en

This brief proposes employing each of the classical 4 transistor (4T) pinned photodiode (PPD) CMOS image sensor (CIS) pixels, for both imaging and temperature measurement, intended for compensating the CISs' dark current, and dark signal non-uniformity (DSNU). The proposed temperature sensors rely on the thermal behavior of MOSFETs working in subthreshold region, when biased with ratiometric currents sequentially. Without incurring any additional hardware or penalty to the CIS, they are measured to have thermal curvature errors less than ±0.3 °C and 3sigma process variations within ±1.3 °C, from 108 sensors on 4 chips, over a temperature range from -20 °C to 80 °C. Each of them consumes 576 nJ/conversion at a conversion rate of 62 samples/s, when quantized by 1 st-order 14 bit delta-sigma ADCs and fabricated using 0.18mu text{m} CIS technology. Experimental results show that they facilitate digital compensation for average dark current and DSNU by 78% and 20%, respectively. @en

In this work, a novel approach for measuring relative temperature variations across the active area of a CMOS image sensor itself is presented. 555 Image pixels have been replaced by temperature sensors pixels (Tixels) in the same pixel array layer. Both sensors, pixels and Tixels, utilize the same readout structure to obtain the data. This approach of measuring temperature variations in the pixel array can be used to compensate for dark signal non-uniformity. Measurements of dark current and temperature have been performed in a temperature range of −40 and 90 °C. Results show that pixels and Tixels are working by using the same readout system based on source followers and column amplifiers. The average dark current of the image sensor increases with temperature in the temperature range of −40 and 60 °C, and at the same time, Tixels show high linear response, having a temperature error less than 0.6 °C after a 1st order best curve fitting.@en

This paper presents an analysis and calibration of process variations for an array of temperature sensors, which are incorporated into a CMOS image sensor chip. Making use of the experimental results of more than 500 temperature sensors implemented on the same chip, the proposed calibration method has removed their process variations from 14.3 % to 2.5 % (3 sigma).@en

In this work, a novel approach is presented for measuring relative temperature variations inside the pixel array of a CMOS image sensor itself. This approach can give important information when compensation for dark (current) fixed pattern noise (FPN) is needed. The test image sensor consists of pixels and temperature sensors pixels (=Tixels). The size of the Tixels is 11 μm × 11 μm. Pixels and Tixels are placed next to each other in the active imaging array and use the same readout circuits. The design and the first measurements of the combined image-temperature sensor are presented. @en

A generic method to reduce the in-line flow dependence of thermal conductivity detectors (TCDs) is presented. The principle is based on a dual-MEMS device configuration. Two thin-film sensors on membranes in parallel in the gas stream on the same chip are differentially operated. Both micro-TCDs are designed to be identical in terms of contact with the main gas flow, however a different depth of the detection chamber results in a different response to the thermal conductivity of the sample gas. Static and dynamic simulations have been performed to characterize the design of the fabricated structures. Devices have been fabricated in a MEMS process using a combined surface- and bulk micromachining process. The devices have been characterized statically and dynamically. Measurements on prototypes show that depending on the range of gases, device size and flow range device the effect of flow on the thermal conductivity can be reduced by a factor 4–15.@en

Conventional thermal conductivity detectors (TCDs) demonstrate a flow dependence. The approach presented here to reduce the flow dependence is based on the on-line flow compensation using two thin-film sensors on membranes in parallel on the same chip that are differentially operated. These are laterally identically, but with a different depth of the detection chamber, resulting in different quasi-static sensitivities to the thermal conductivity of the sample gas. The effects of conduction and convection in the structure have been studied using COMSOL Multiphysics. First prototypes have been fabricated and are presently tested.@en