Browsing by Subject "Transistors"

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Open Access
Demonstration of flexible thin film transistors with GaN channels
(American Institute of Physics Inc., 2016) Bolat, S.; Sisman, Z.; Okyay, Ali Kemal
We report on the thin film transistors (TFTs) with Gallium Nitride (GaN) channels directly fabricated on flexible substrates. GaN thin films are grown by hollow cathode plasma assisted atomic layer deposition (HCPA-ALD) at 200 °C. TFTs exhibit 103 on-to-off current ratios and are shown to exhibit proper transistor saturation behavior in their output characteristics. Gate bias stress tests reveal that flexible GaN TFTs have extremely stable electrical characteristics. Overall fabrication thermal budget is below 200 °C, the lowest reported for the GaN based transistors so far. © 2016 Author(s)
Open Access
High-frequency performance of submicrometer transistors that use aligned arrays of single-walled carbon nanotubes
(American Chemical Society, 2009-04-08) Kocabaş, Coşkun; Dunham, S.; Cao, Q.; Cimino, K.; Ho, X.; Kim, H.-S.; Dawson, D.; Payne, J.; Stuenkel, M.; Zhang, H.; Banks, T.; Feng, M.; Rotkin, S. V.; Rogers, J. A.
The unique electronic properties of single-walled carbon nanotubes (SWNTs) make them promising candidates for next generation electronics, particularly in systems that demand high frequency (e.g., radio frequency, RF) operation. Transistors that incorporate perfectly aligned, parallel arrays of SWNTs avoid the practical limitations of devices that use individual tubes, and they also enable comprehensive experimental and theoretical evaluation of the intrinsic properties. Thus, devices consisting of arrays represent a practical route to use of SWNTs for RF devices and circuits. The results presented here reveal many aspects of device operation in such array layouts, including full compatibility with conventional small signal models of RF response. Submicrometer channel length devices show unity current gain (ft) and unity power gain frequencies (fmax) as high as ∼5 and ∼9 GHz, respectively, with measured scattering parameters (S-parameters) that agree quantitatively with calculation. The small signal models of the devices provide the essential intrinsic parameters: saturation velocities of 1.2 × 107 cm/s and intrinsic values of ft of ∼30 GHz for a gate length of 700 nm, increasing with decreasing length. The results provide clear insights into the challenges and opportunities of SWNT arrays for applications in RF electronics.
Open Access
Imaging capability of pseudomorphic high electron mobility transistors, AlGaN/GaN, and Si micro-Hall probes for scanning Hall probe microscopy between 25 and 125 °c
(American Vacuum Society, 2009) Akram, R.; Dede, M.; Oral, A.
The authors present a comparative study on imaging capabilities of three different micro-Hall probe sensors fabricated from narrow and wide band gap semiconductors for scanning hall probe microscopy at variable temperatures. A novel method of quartz tuning fork atomic force microscopy feedback has been used which provides extremely simple operation in atmospheric pressures, high-vacuum, and variable-temperature environments and enables very high magnetic and reasonable topographic resolution to be achieved simultaneously. Micro-Hall probes were produced using optical lithography and reactive ion etching process. The active area of all different types of Hall probes were 1×1 μ m2. Electrical and magnetic characteristics show Hall coefficient, carrier concentration, and series resistance of the hall sensors to be 10 mG, 6.3× 1012 cm-2, and 12 k at 25 °C and 7 mG, 8.9× 1012 cm-2 and 24 k at 125 °C for AlGaNGaN two-dimensional electron gas (2DEG), 0.281 mG, 2.2× 1014 cm-2, and 139 k at 25 °C and 0.418 mG, 1.5× 1014 cm-2 and 155 k at 100 °C for Si and 5-10 mG, 6.25× 1012 cm-2, and 12 k at 25 °C for pseudomorphic high electron mobility transistors (PHEMT) 2DEG Hall probe. Scan of magnetic field and topography of hard disc sample at variable temperatures using all three kinds of probes are presented. The best low noise image was achieved at temperatures of 25, 100, and 125 °C for PHEMT, Si, and AlGaNGaN Hall probes, respectively. This upper limit on the working temperature can be associated with their band gaps and noise associated with thermal activation of carriers at high temperatures.
Open Access
In-situ focused ion beam implantation for the fabrication of a hot electron transistor oscillator structure
(1996) Kaya I.I.; Dellow, M.W.; Bending, S.J.; Linfield, E.H.; Rose P.D.; Ritchie, D.A.; Jones G.A.C.
Recent advances using in situ focused ion beam implantation during an MBE growth interruption have been exploited to fabricate planar GaAs hot electron structures without the need for shallow ohmic contacts. This novel fabrication route shows a very high yield and has been used to demonstrate a prototype high-frequency oscillator structure based on electron multiplication in the base layer. Existing devices show transfer factors in excess of unity as well as reversal of the base current at high injection levels, which are the prerequisites for oscillator action. Future improvements in device design are discussed.
Open Access
Quantum mechanical simulation of charge transport in very small semiconductor structures
(IEEE, 1989) Yalabik, M. C.; Diff, K.
A quantum mechanical simulation method of charge transport in very small semiconductor devices, based on the numerical solution of the time-dependent Schrödinger equation (coupled self-consistently to the Poisson equation to determine the electrostatic potential in the device), is presented. Carrier transport is considered within the effective mass approximation, while the effects of the electron-phonon interaction are included in an approximation that is consistent with the results of the perturbation theory and gives the correct two-point time correlation function. Numerical results for the transient behavior of a planar ultrasubmicrometer three-dimensional GaAs MESFET (gate length of 26 nm) are also presented. They indicate that extremely fast gate-step response times (switching times) characterize such short-channel GaAs devices. © 1989 IEEE