Implementing a-IGZO Thin-Film Transistors on Thin Ceramic Substrates to Reduce Self-Heating Effects

In recent years, amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) have proliferated in both small-scale research and industry products due to the metal oxide’s beneficial properties. IGZO’s optical transparency, high and tunable mobility, and relatively low cost has made it an appealing candidate for use in applications ranging from gas sensors to electronic backplane arrays. However, the stability of a-IGZO TFTs is limited by the degree to which such devices’ electrical performance varies with changes in factors like operation temperature. For this reason, the reliability of a-IGZO TFTs can be improved by reducing the amount of self-heating that the transistors experience due to Joule heating and other effects. <br/>Previous investigations have focussed on mitigating the self-heating effect by altering the structure or driving conditions of the TFT itself. While TFT modifications, such as restricting the bias voltage and frequency or tuning the channel width, can reduce self-heating, methods of reducing device temperature that are independent of or work in conjunction with TFT structure and operation adjustments could be beneficial. For example, building TFTs on a substrate that significantly reduces self-heating would allow device optimization efforts to concentrate on other improvements, such as increasing mobility.<br/>Recent work has shown that thin, thermally-conductive substrates can be used as passive heat-sinks for microLEDs. MicroLEDs built on 80 um-thin Corning Alumina Ribbon Ceramic demonstrated less self-heating and less external quantum efficiency (EQE) reduction compared to microLEDs built on standard glass substrates during both I-V speed curve and drive time tests. Additionally, the microLEDs built on the ceramic substrate outperformed those built on glass during destruction testing, exhibiting superior optical power outputs at higher driving currents [3]. While the mechanisms contributing to the self-heating of microLEDs are not identical to those affecting TFTs, heat-sinking a significant portion of the thermal energy generated by the Joule heating effect prior to the deterioration of electrical characteristics would improve TFT stability regardless of device structure or biasing conditions.<br/>In this work, we explore ongoing efforts to reduce self-heating in a-IGZO TFTs by implementing them on thin ceramic substrates. The extent to which the devices are experiencing self-heating under standard and stressed biasing conditions is quantified by analyzing the current droop visible on the TFT I-V curves, corroborated using infrared thermal imaging techniques, and compared to the performance of identically-structured a-IGZO TFTs built on thicker glass substrates. Additionally, the degree to which the thickness of the ceramic substrate affects TFT stability is analyzed, and reliability improvements across different TFT structures, compositions, and operation environments are normalized to assess the extent to which ceramic heat-sinking could benefit a variety of metal oxide TFT applications.