Heiko Frenzel

Recent Progress on ZnO‐Based Metal‐Semiconductor Field‐Effect Transistors and Their Application in Transparent Integrated Circuits

Metal-semiconductor field-effect transistors (MESFETs) are widely known from opaque high-speed GaAs or high-power SiC and GaN technology. For the emerging field of transparent electronics, only metal-insulator-semiconductor field-effect transistors (MISFETs) were considered so far. This article reviews the progress of high-performance MESFETs in oxide electronics and reflects the recent advances of this technique towards transparent MESFET circuitry. We discuss design prospects as well as limitations regarding device performance, reliability and stability. The presented ZnO-based MESFETs and inverters have superior properties compared to MISFETs, i.e., high channel mobilities and on/off-ratios, high gain, and low uncertainty level at comparatively low operating voltages. This makes them a promising approach for future low-cost transparent electronics.

ZnO metal-semiconductor field-effect transistors with Ag-Schottky gates

Metal-semiconductor field-effect transistors (MESFETs) were fabricated by reactive dc sputtering of Ag-Schottky gate contacts on ZnO thin-film channels grown by pulsed-laser deposition on sapphire. The n-type conductivity (normally on) of typical MESFETs is tunable over 8 decades in a voltage range of 2.5V with an off voltage of −1.5V and very low off-current density in the range of 10−6A∕cm2. Channel mobilities of up to 27cm2∕Vs have been achieved.

Low-temperature processed Schottky-gated field-effect transistors based on amorphous gallium-indium-zinc-oxide thin films

We have investigated the electrical properties of metal-semiconductor field-effect transistors (MESFET) based on amorphous oxide semiconductor channels. All functional parts of the devices were sputter-deposited at room temperature. The influence on the electrical properties of a 150 °C annealing step of the gallium-indium-zinc-oxide channel is investigated. The MESFET technology offers a simple route for processing of the transistors with excellent electrical properties such as low subthreshold swing of 112 mV/decade, gate sweep voltages of 2.5 V, and channel mobilities up to 15 cm2/V s.

Ferroelectric thin film field-effect transistors based on ZnO/BaTiO3 heterostructures

The authors have grown epitaxial ZnO/BaTiO3 (BTO) heterostructures by pulsed laser deposition on lattice matched Nb-doped SrTiO3 substrates. Epitaxial growth of the BTO layers has been confirmed by x-ray diffraction. The electrical properties of ZnO/BTO heterostructures have been investigated by current-voltage and capacitance-voltage measurements, showing that the BTO layers are highly insulating (leakage current density jl<10−9 A/cm2 at 5 V). The structures were processed into field-effect transistors, and their output and transfer properties have been determined. A large memory effect of the source-drain current on the previously applied “programm” gate voltage (−7 or +20 V) has been observed. It is reproducible in repeated switching cycles, showing the suitability of the structure as a nonvolatile memory device.

High-gain integrated inverters based on ZnO metal-semiconductor field-effect transistor technology

We report on the design and fabrication of ZnO-based integrated inverters consisting of normally-on metal-semiconductor field-effect transistors and AgxO Schottky diodes as level shifters. The inverters show high gain values up to 197 at 3 V operating voltage and low uncertainty levels in the range of 0.13 V. The influence of the level shifter and the channel material/thickness on the performance of the inverters has been investigated. Using Zn0.997Mg0.003O for the channel thin film leads to high reproducibility (90%) of the devices. A logic NOR-gate has been implemented showing the possibility to fabricate a complete logic.

Mott variable-range hopping and weak antilocalization effect in heteroepitaxial Na 2 IrO 3 thin films

Iridate thin films are a prerequisite for any application utilizing their cooperative effects resulting from the interplay of strong spin-orbit coupling and electronic correlations. Here, heteroepitaxial

ZnO-Based n-Channel Junction Field-Effect Transistor With Room-Temperature-Fabricated Amorphous p-Type

{\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}

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thin films with (001) out-of-plane crystalline orientation and well-defined in-plane epitaxial relationship are presented on various oxide substrates. Resistivity is dominated by a three-dimensional variable-range hopping mechanism in a large temperature range between 300 K and 40 K. Optical experiments show the onset of a small optical gap

Gate

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