|Ph.D Student||Zviagintsev Alex|
|Subject||Uncooled Passive IR Sensors and Small Arrays Based on|
|Department||Department of Electrical Engineering||Supervisors||Professor Emeritus Yael Nemirovsky|
|Dr. Ilan Bloom|
|Full Thesis text|
A novel thermal sensor based on a suspended transistor made in a standard CMOSSOI process and released by dry etching, has been developed at Technion. The uncooled IR sensing is based on a thermally isolated floating transistor (TMOS), which senses temperature change, by changes in the transistor I-V characteristics. Using the transistor as an active sensing element has advantages in terms of internal gain multiplexing within the sensor and high temperature sensitivity.
IR sensing using TMOS as sensor requires a multidimensional intensive research and analysis. The scientific-academic aspects of the research are reflected in new concepts and approaches that have been invented to meet the following challenges: considerable detector noise; low minimum signal; process and circuit based non-uniformities; pixel self-heating; and transistor operation modes. The conventional approach to circuit noise reduction cannot be directly applied following the established methodology because the signal, which is the temperature, cannot be switched off and because the thermal sensors are relatively slow. New approaches combine physical, mechanical, thermal and electrical considerations from the very early steps of the design, enabling a tremendous improvement in the sensor and integrated circuit performance.
In this work we investigate the TMOS sensor and some applications based on voltage, current and novel charge sensing. We analyzed the performance dependence on sensor geometry configuration and operation mode combined with signal readout principles; self-heating effect; in air operation; adaptive external biasing and power dissipation.
For the first time, we have researched and developed complete and effective models, that are extremely important as a design tool for systems, employing unique TMOS sensors integrated monolithically with readout. We demonstrate, that as an active element with internal gain, TMOS is outstanding in temperature response and achieves competitive performance.
We modeled and analyzed the mosaic pixel configuration, composed of several TMOS sensors, which are electrically connected, either in parallel or in series, as well as a combination of both options. Compared to a single TMOS per pixel design, mosaic configuration allows one to design pixels with an extremely large field of views, while mechanical strength and thermal time-constant remain the same.
We propose a novel and effective methods for self-heating effect compensation based either on a new reference pixel configuration operated by short-pulses or on external adaptive biasing with increased dynamic range, that removes the necessity of the reference cells.
We also presented and analyzed a new approach for uncooled thermal imaging - charge sensing. The new concept is based on temperature dependence of TMOS capacitor in weak inversion, that is outstanding for its extremely ultra-low power dissipation (order of nWatt) and negligible self-heating effect, which makes it very attractive for long-time battery applications.
In conclusion, this study suggests, that uncooled thermal systems based on TMOS sensors may achieve performance, competitive with state of the art commercially available systems. Moreover, TMOS sensors, operated in sub-threshold, are superior in power dissipation and significantly decreased self-heating effect. Accordingly, this uncooled IR sensor may become the standard PIR technology for mobile applications, wearables and Internet of Things (IoT).