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Register a new userField Effect Transistor Based on KTaO3 Perovskite
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An n-channel accumulation-type field effect transistor (FET) has been fabricated utilizing a KTaO3 single crystal as an active element and a sputtered amorphous Al2O3 film as a gate insulator. The device demonstrated an ON/OFF ratio of 10^4 and a field effect mobility of 0.4cm^2/Vs at room temperature, both of which are much better than those of the SrTiO3 FETs reported previously. The field effect mobility was almost temperature independent down to 200K. Our results indicate that the Al2O3 / KTaO3 interface is worthy of further investigations as an alternative system of future oxide electronics.
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We show herein fabrication and field-modulated thermopower for KTaO3 single-crystal based field-effect transistors (FETs). The KTaO3 FET exhibits field effect mobility of ~8 cm2/Vs, which is ~4 times larger than that of SrTiO3 FETs. The thermopower of the KTaO3 FET decreased from 600 to 220 microV/K by the application of gate electric field up to 1.5 MV/cm, ~400 microV/K below that of an SrTiO3 FET, clearly reflecting the smaller carrier effective mass of KTaO3.
Fundamental physical properties limiting the performance of spin field effect transistors are compared to those of ordinary (charge-based) field effect transistors. Instead of raising and lowering a barrier to current flow these spin transistors use static spin-selective barriers and gate control of spin relaxation. The different origins of transistor action lead to distinct size dependences of the power dissipation in these transistors and permit sufficiently small spin-based transistors to surpass the performance of charge-based transistors at room temperature or above. This includes lower threshold voltages, smaller gate capacitances, reduced gate switching energies and smaller source-drain leakage currents.
The celebrated electronic properties of graphene have opened way for materials just one-atom-thick to be used in the post-silicon electronic era. An important milestone was the creation of heterostructures based on graphene and other two-dimensional (2D) crystals, which can be assembled in 3D stacks with atomic layer precision. These layered structures have already led to a range of fascinating physical phenomena, and also have been used in demonstrating a prototype field effect tunnelling transistor - a candidate for post-CMOS technology. The range of possible materials which could be incorporated into such stacks is very large. Indeed, there are many other materials where layers are linked by weak van der Waals forces, which can be exfoliated and combined together to create novel highly-tailored heterostructures. Here we describe a new generation of field effect vertical tunnelling transistors where 2D tungsten disulphide serves as an atomically thin barrier between two layers of either mechanically exfoliated or CVD-grown graphene. Our devices have unprecedented current modulation exceeding one million at room temperature and can also operate on transparent and flexible substrates.
We study the effects of low-energy electron beam irradiation up to 10 keV on graphene based field effect transistors. We fabricate metallic bilayer electrodes to contact mono- and bi-layer graphene flakes on SiO$_2$, obtaining specific contact resistivity $rho_c simeq 19 kOmega mu m^2$ and carrier mobility as high as 4000 cm$^2$V$^{-1}$s$^{-1}$. By using a highly doped p-Si/SiO$_2$ substrate as back gate, we analyze the transport properties of the device and the dependence on the pressure and on the electron bombardment. We demonstrate that low energy irradiation is detrimental on the transistor current capability, resulting in an increase of the contact resistance and a reduction of the carrier mobility even at electron doses as low as 30 $e^-/nm^2$. We also show that the irradiated devices recover by returning to their pristine state after few repeated electrical measurements.
We present an analytical device model for a graphene bilayer field-effect transistor (GBL-FET) with a graphene bilayer as a channel, and with back and top gates. The model accounts for the dependences of the electron and hole Fermi energies as well as energy gap in different sections of the channel on the bias back-gate and top-gate voltages. Using this model, we calculate the dc and ac source-drain currents and the transconductance of GBL-FETs with both ballistic and collision dominated electron transport as functions of structural parameters, the bias back-gate and top-gate voltages, and the signal frequency. It is shown that there are two threshold voltages, $V_{th,1}$ and $V_{th,2}$, so that the dc current versus the top-gate voltage relation markedly changes depending on whether the section of the channel beneath the top gate (gated section) is filled with electrons, depleted, or filled with holes. The electron scattering leads to a decrease in the dc and ac currents and transconductances, whereas it weakly affects the threshold frequency. As demonstrated, the transient recharging of the gated section by holes can pronouncedly influence the ac transconductance resulting in its nonmonotonic frequency dependence with a maximum at fairly high frequencies.
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