Design and characterization of polysilicon TFT devices, circuits and systems for large area flexible electronic applications

Polysilicon TFT technology shown to be an excellent alternative to amorphous silicon technology for high performance, high quality and low power, small and mid size flat panel mobile displays. Reliable performance of polysilicon TFT electronics made it the potential technology of choice for several other large area matrix-based applications such as transducers and sensors as well.;This dissertation addresses various aspects of the design and characterization of polysilicon thin film transistor (TFT) electronics with the main focus on development of large area systems on flexible platform. This includes evaluation of polysilicon TFT devices on stainless steel foil as far as scalability, matching, uniformity, stability and their comparability with devices on rigid platform. At a higher level this work addresses the design and performance characterization of pixel circuits for matrix based systems. Two distinct applications of actuators and sensors are considered in this part. A high voltage, high current TFT device is engineered to be a part of the pixel circuit of a matrix-based actuator system (that is used for printing applications). Double and triple gate TFT devices are structured to withstand OFF-state drain to source voltage of more that 35V while capable of providing 50mA of current at ON-state. Furthermore voltage noise of lateral polysilicon PIN diodes which are employed as part of the pixel circuit of a thermal sensing system is also studied. It is demonstrated through experiments that voltage noise of PIN diodes are strongly depends on the polysilicon grain size and quality. Additionally, voltage noise also relates to the thickness of the polysilicon as the active material. As the grain size decreases the voltage noise of PIN diodes tends to increase however as the thickness of the active material increases cause the voltage noise to decrease. Furthermore, voltage noise strongly depends on the i-region width and length; it tends to increase with increasing i-region length and to decrease with increasing i-region width. Methods to improve the voltage noise of lateral polysilicon PIN diodes are also proposed and experiment results are revealed.;This effort also demonstrates several electronic circuits to be used as scanning, controlling and processing circuit blocks of large area electronic systems utilizing polysilicon TFT technology. Exploiting polysilicon TFT assets, these circuit blocks improve upon existing digital, analog and mixed signal circuits while complying with the limitations of polysilicon TFT as a novel technology as well as flexible substrates. High performance circuits including 3-bit flash analog to digital converter, 5-bit R-2R digital to analog converter, Full-bit shift registers, decoders and 21 different adder cells are demonstrated with SLS polysilicon TFT technology on stainless steel foil substrate. Furthermore design and development of a 4-bit Harvard structure microprocessor (CPU) as well as a high gain operational amplifier with polysilicon TFT technology are also discussed. These circuits can be integrated on the same monolithic substrate as the large area system to improve the system integration level.;Finally this work addresses the effect of mechanical strain on the performance of polysilicon TFT devices and ring oscillators on flexible steel foil substrate. Majority of flexible electronic applications require considerable amount of flexibility and conformability which may lead to substantial amount of stress on electronic circuits. We have realized that as the longitudinal mechanical tensile (compressive) strain increases mobility of n-type TFTs increases (decreases) and that of p-type decreases (increases). Propagation delay of ring oscillators on the other hand tends to drop with tensile and increase with compressive strain, almost linearly. Realizing the effect of mechanical strain on the performance flexible polysilicon TFT electronics potentially aid to find solutions to compensate for unwanted changes.;The main objective of this endeavor is to further advance the polysilicon TFT technology and demonstrate its capabilities and also prove its compatibility with variety of substrates by successful development of polysilicon TFT devices, circuits and systems, for different applications, on unconventional rigid (quartz) as well as flexible (stainless steel foil) platforms.