A simplified device structure for depletion-mode organic thin film transistors is described in which the gate electrode and the source/drain contacts are prepared in the same process step, thus reducing the number of material depositions and photolithography steps. Based on the simplified device structure and using the small-molecule aromatic hydrocarbon pentacene as the active material, organic thin film transistors were fabricated on glass substrates with carrier mobility of 0.6 cm2/V s, on/off current ratio of 105, and subthreshold slope of 0.5 V/decade.
Using a thermal mountant, we have fabricated hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) and integrated circuits on both colored and nearly colorless polyimide substrates with performance very similar to devices fabricated on glass substrates. Delay and power dissipation were measured with ring oscillators; minimum stage delay was less than 10 psec, and minimum power dissipation was less than 10 pW per stage. These results indicate that with suitable thermal engineering, a-Si:H devices and circuits can be fabricated on polymeric substrates using nearly standard processing.
We discuss the many factors affecting the reliability of GaAs HBTs that we have encountered starting from the early days of AlGaAs-emitter HBTs through the present day use of InGaP-emitter HBTs. We discuss both wearout and infancy failure modes and try to distinguish fundamental (i.e., unavoidable) from nonfundamental failure modes. We have found that infant failures are dominated by substrate dislocation density, which can limit long-term-reliable circuit sizes to under ~1000 transistors.
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