Diane Carol Freeman

Stable ZnO thin film transistors by fast open air atomic layer deposition

We report stable, high performance zinc oxide thin film transistors grown by an atmospheric pressure atomic layer deposition system. With all deposition and processing steps kept at or below 200°C, the alumina gate dielectric shows low leakage (below 10−8A∕cm2) and high breakdown fields. Zinc oxide thin film transistors in a bottom gate geometry yield on/off ratios above 108, near zero turn-on voltage, little or no hysteresis, and mobility greater than 10cm2∕Vs. With alumina passivation, shifts in threshold voltage under gate bias stress compare favorably to those reported in the literature.We report stable, high performance zinc oxide thin film transistors grown by an atmospheric pressure atomic layer deposition system. With all deposition and processing steps kept at or below 200°C, the alumina gate dielectric shows low leakage (below 10−8A∕cm2) and high breakdown fields. Zinc oxide thin film transistors in a bottom gate geometry yield on/off ratios above 108, near zero turn-on voltage, little or no hysteresis, and mobility greater than 10cm2∕Vs. With alumina passivation, shifts in threshold voltage under gate bias stress compare favorably to those reported in the literature.

Oxide Electronics by Spatial Atomic Layer Deposition

We report on zinc oxide (ZnO)-based devices produced by a fast, open-air atomic layer deposition (ALD) process relying upon the spatial isolation of reactive gases. At deposition rates of greater than 100 Aring per minute, ZnO-based thin-film transistors by spatial atomic layer deposition (S-ALD) show mobility above 15 cm2/Vs and excellent stability. Measurement and modeling of the gas isolation in the deposition head is discussed. Saturation curves obtained for aluminum oxide (Al2O3) growth using trimethylaluminum and water are shown to be consistent with chamber ALD systems. Finally, the ability of this new ALD process to leverage patterning by using poly(methyl methacrylate) (PMMA) as a growth inhibitor for selective area deposition is discussed. Relatively thin films of PMMA (~ 40 Aring) are shown to be capable of inhibiting the growth of ZnO for at least 1200 ALD cycles.

Pentacene TFT driven AM OLED displays

Pentacene organic thin-film transistors (TFTs)-driven active matrix organic light-emitting diode (OLED) displays has been investigated. This letter addresses several process issues unique to this type of display which are important in achieving bright and uniform displays. A bottom contact structure was used to fabricate the pentacene TFT backplane. Polyvinyl alcohol and parylene were used to isolate the pentacene active layer and passivate the backplane. The low processing temperature may allow the use of polymeric substrates and lower cost processing. Uniform TFT performance is achieved with reasonably good mobility and on/off ratio on the backplane. The initial OLED display performance is also presented.

ZnO Thin-Film Transistor Ring Oscillators with 31-ns Propagation Delay

We have fabricated ring oscillators (ROs) using ZnO thin films deposited by using a spatial atomic layer deposition process at atmospheric pressure and low temperature (200degC). Bottom-gate thin-film transistors with aluminum source and drain contacts were fabricated with a field-effect mobility of > 15 cm2/V ldr s. Seven-stage ROs operated at a frequency as high as 2.3 MHz for a supply voltage of 25 V, corresponding to a propagation delay of 31 ns/stage. These circuits also had propagation delays of ~100 ns/stage at a supply voltage of 15 V. To the best of our knowledge, these are the fastest ZnO circuits reported to date.

All-organic Active Matrix OLED Flexible Display

We have fabricated pentacene organic thin-film transistor (OTFT) driven active matrix organic light-emitting diode (OLED) displays on both glass and flexible polyethylene terephthalete (PET) substrates. These displays have 48 × 48 bottom-emission OLED pixels with two pentacene OTFTs used per pixel. Polyvinyl alcohol (PVA) and parylene were used to photolithographically pattern the pentacene active layer and isolate the OTFT backplane from the OLEDs. Pentacene OTFTs are able to easily supply the current required for OLED operation, but improvements in device uniformity and stability are of interest.

ZnO Thin Film Transistor Ring Oscillators with sub 75 nsec Propagation Delay

We have fabricated simple circuits, including ring oscillators, using ZnO thin films deposited by low temperature (200degC) atmospheric pressure chemical vapor deposition. Bottom gate TFTs with aluminum source and drain contacts typically had field effect mobility >15 cm2/Vs. Seven stage ring oscillators operated at frequency as high as 1 MHz for a supply voltage of 32 V, corresponding to a propagation delay less than 75 nsec/stage. These circuits also had propagation delay less than 150 ns/stage at a supply voltage of 18 V. To our knowledge, these are the fastest ZnO circuits reported to date.

Fast ZnO Thin-Film Transistor Circuits

We report here five-stage ring-oscillator-integrated circuits fabricated using ZnO TFTs with signal propagation delays as low as 100 ns (>1 MHz oscillation frequency) for a 45 V supply voltage. These circuits also operate at a supply voltage as low as 10 V. To our knowledge, these are the fastest ZnO integrated circuits reported to date. We also designed ring oscillators with different source/gate and drain/gate overlap to investigate aspects of the circuit speed.

Uniform ZnO Thin-Film Transistors by an Ambient Process

We have fabricated zinc oxide thin-film transistors using a novel ambient deposition process, with maximum temperature of 200degC. The TFTs deposited this way show sufficiently good properties to make them potentially applicable to OLED display backplanes.

P-196L: Late-News Poster: High-Performance Zinc Oxide Transistors by an Ambient Process

An ambient process was developed for producing both the dielectric and semiconductor layers of a zinc oxide-based thin-film transistor. The dielectric films exhibited good electrical properties, leading to devices with gate leakage less than 25 nA/cm2. Typical devices had mobilities in excess of 5 cm2/Vs from a process with a maximum substrate temperature of 200°C. In addition, devices showed reasonable electrical stability in this novel deposition process for dielectrics and semiconductors.

All-organic active matrix oled display

This paper reports on 48 times 48 pixels pentacene TFT driven active-matrix OLED displays on glass substrate. To our best knowledge these are the largest pentacene TFT driven displays