The authors investigate 2μm gate-length InAlN∕GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS HEMTs) with 12nm thick Al2O3 gate insulation. Compared to the Schottky barrier (SB) HEMT with similar design, the MOS HEMT exhibits a gate leakage reduction by six to ten orders of magnitude. A maximal drain current density (IDS=0.9A∕mm) and an extrinsic transconductance (gme=115mS∕mm) of the MOS HEMT also show improvements despite the threshold voltage shift. An analytical modeling shows that a higher mobility of electrons in the channel of the MOS HEMT and consequently a higher number of electrons attaining the velocity saturation may explain the observed increase in gme after the gate insulation.
Titanium dioxide thin films were grown on RuO 2 layers by atomic layer deposition. The stabilizing effect of the bottom rutile-type RuO 2 layer resulted in growth of the TiO 2 rutile films at temperatures above 275°C. Stabilization of the TiO 2 rutile phase occurred due to local epitaxial growth of the polycrystalline RuO 2 /TiO 2 /RuO 2 structure, as revealed by transmission electron microscopy. A dielectric constant as high as 155 and equivalent oxide thickness ͑EOT͒ as low as 0.5 nm were determined from the capacitance-voltage measurements for the TiO 2 films grown above 275°C. A leakage current density of 10 −3 A/cm 2 at 1 V bias voltage was obtained for the films with EOT equal to 0.5 nm.Titanium dioxide is an attractive dielectric material for microelectronic applications. Depending on its growth conditions, TiO 2 can be most easily prepared in amorphous, anatase, and/or rutile phases. The rutile phase exhibits very high dielectric constant, ranging from 90 to 170, depending on the lattice orientation. 1 Due to the high dielectric constant, the TiO 2 rutile phase is considered a promising material for capacitors in future generations of dynamic random access memories ͑DRAMs͒. 2 Unfortunately, rutile often coexists in thin films with lower dielectric constant TiO 2 phase, i.e., anatase, thereby resulting in a reduction of effective dielectric constant. Postdeposition annealing at temperatures above 800°C has to be performed to obtain pure rutile phase films. 3-5 However, it was shown that the growth of phase-pure rutile films at low temperatures can be stabilized by choice of an appropriate substrate. For instance, by using atomic layer deposition ͑ALD͒ and TiCl 4 and H 2 O as precursors, pure rutile films have been grown on ͑1-102͒-oriented sapphire substrates at 425°C. 6 Recently, Kim, et al. demonstrated ALD growth of TiO 2 rutile film at even lower temperatures on a Ru substrate pretreated by O 3 . 7 This pretreatment of the Ru electrode resulted in a thin surface film of RuO 2 with the structure compatible to that of the TiO 2 rutile phase. Using this approach, TiO 2 films with a dielectric constant of 100 were prepared at temperature as low as 250°C. 8 In a DRAM capacitor dielectric film should be combined with conductive electrodes. As the affinity of TiO 2 is about 4 eV, 9 metals with high work function should be used as electrodes to prevent excessive leakage currents due to Schottky emission. We have recently demonstrated that the work function of ruthenium oxide is more than 5 eV. 10 RuO 2 has high conductivity and crystallizes in the rutile structure with the lattice parameters ͑a RuO 2 = 0.4499 nm, c RuO 2 = 0.3107 nm͒ close to that of the TiO 2 rutile phase ͑a TiO 2 = 0.4593 nm, c TiO 2 = 0.2959 nm͒. Therefore, RuO 2 is a promising material for electrodes in capacitors with TiO 2 dielectric. In our work we have extended the approach of Kim et al. 7 to use RuO 2 as a seed layer for the TiO 2 rutile phase growth. Instead of oxidizing the Ru surface to obtain RuO 2 , we have used bottom polycrysta...
Articles you may be interested inImpact of crystallization behavior of Sr x Ti y O z films on electrical properties of metal-insulator-metal capacitors with TiN electrodes Appl. Phys. Lett. 97, 162906 (2010); 10.1063/1.3505323Effect of annealing and electrical properties of high-κ thin films grown by atomic layer deposition using carboxylic acids as oxygen source
The reactivities of several oxide materials (OM) in direct contact with BSCCO powder has been tested at a temperature of approximately 845 • C in air. The OM such as BaZrO 3 , SrCO 3 , MgO and ZrO 2 showing little or no reactivity with BSCCO were mixed (10 wt%) with a BSCCO precursor powder and used for monocore tapes made by a standard powder-in-tube technique. The microstructure of the BSCCO+OM cores was analysed by SEM and XRD and the transport current properties-critical current, pinning force and resistance up to 16 T-were measured as a function of the magnetic field for various orientations with respect to the ab plane. The OM used influenced the electrical properties of the Bi-2223 phase in different ways. This is because the oxides react with BSCCO during the heat treatment and simultaneously affect the 2212 → 2223 phase transformation as well as the Bi-2223 grain growth and grain connectivity. Submicrometre commercial SrCO 3 powder was evaluated as the best material from all those tested, for resistive barriers in Bi-2223/Ag tapes.
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