A room temperature oxide channel field effect transistor with the channel on the surface was recently demonstrated at IBM which showed switching characteristics similar to conventional silicon FETs. In this paper we introduce a new architecture for the oxide channel transistor where the oxide channel material is buried below the gate oxide layer. This buried channel architecture has several significant advantages over the surface channel design in coupling capacitance, channel mobility, and channel stability. We will discuss the design and fabrication of the buried channel oxide FET and we will present results from these devices which demonstrate a higher transconductance.

We describe simulations on a simplified design for a metal-oxide nanoscale Field Effect Transistor (FET). The device features an oxide channel with a high dielectric constant ferroelectric as the gate insulator. In the present model, the gate and source/drain electrodes are unconventionally placed on opposite sides of the channel. Simulations are quantum mechanical and are based on a simplified transport model. Results on a 10 nm. channel device show adequate conductance and ON/OFF ratio, while simulation of a ring oscillator yields an estimated device switching time of 300 fs..

In this paper we describe improved methods of fabrication for an oxide channel field effect transistor (OxFET) similar in architecture to a conventional FET. We demonstrate that a substrate treatment consisting of a low power oxygen ashing followed by annealing yields a strontium (A-site) terminated surface in single-crystal strontium titanate (STO). This surface termination of the substrate results in pulsed laser deposited cuprate-channel films of improved quality.

Pt/SBT/TiO2/Si structure was proposed for metal/ferroelectric/insulator/semiconductor field effect transistor (MFIS-FET) applications. SrBi2.4 Ta2O9 (SBT) thin films of 400 nm thickness were prepared using liquid source misted chemical deposition (LSMCD) on Si(100) substrates with TiO2 buffer layers deposited by DC reactive sputtering with the thickness ranging from 5 nm to 200 nm and electrical properties of MFIS structures were investigated. Memory window and maximum capacitance of the Pt/SBT/TiO2 /Si structure increased with decreasing the thickness of TiO2 buffer layer. The Pt/SBT(400 nm)/TiO2(10 nm)/Si structure exhibited C-V hysteresis loop with the memory window of 1.6 V at ±5 V, and could be applicable for MFISFET applications.

In order to search for efficient target materials for use in Hyperthermal Surface lonisation (HSI), a new mass spectroscopy ionisation technique, we have performed a study of high and low work function (ø) surfaces as part of an ongoing project. HSI relies on high and low work function surfaces for the production of positive (pHSI) and negative (nHSI) ions, respectively.

Using a novel UHV Scanning Kelvin Probe we have followed the oxidation kinetics of polycrystalline Re at different temperatures and examined the effects of oxidation, flash annealing and sputter-anneal cleaning cycles via high resolution work function topographies. Our results indicate that oxidised Re is the best candidate for pHSI in terms of ionisation efficiency and ø change. The peak work function change of 2.05 eV occurred at 900 K to 950K.

For the nHSI materials Calcium exhibited the best performance with respect to the ionisation efficiency indicating a wf of 2.9 eV. We will present data in terms of mass fragmentation using an HSI-Time-of-Flight (TOF) system and time stability of the work function.

Utilizing a chemical transport reaction, we succeeded in growing large and clean anatase TiO2 single crystals whose surfaces could be characterized by standard physical and electro-chemical techniques. The examination of the structure of the clean (101) and (001) faces by low energy electron diffraction (LEED) and secondary electron imaging (SEI) showed that these surfaces are bulk terminated and thermodynamically stable. Impedance spectroscopy in aqueous solution revealed a slight difference in the flatband potential between the (101) and the (001) faces. This shift is also manifested in a different photocurrent onset potential and can be rationalized by a different water adsorption on the two surface structures. Voltammetry in aprotic solutions showed a different lithium insertion behavior for the two surfaces. This is explained by a different structural transparency of the anatase lattice in the two directions. Both findings favor the (001) over the (101) surface. These orientational dependencies may have some important technological relevance for the mesoscopic TiO2 films used in solar cells and lithium batteries.

Recent experiments revealed an apparently bias-dependent tunneling magnetoresistance between a transition metal (such as Fe, Co) and an oxide barrier such as SrTiO3. We examine the materials issues involved in this type of hybrid transition metal-oxide junctions. The junction interface is shown to be unstable against thermal treatment or high-bias current stress. We conclude that the junction magnetoresistance is largely determined by the formation of an interface oxide layer different from the barrier or the transition metal electrode themselves.

After growing black colored single crystals of LixNi1−xO (x = 0.27) and solving its crystal structure, a model is proposed as an alternative to the structural type admitted for LixNi1−xO. The new rhombohedral cell consists of a cubic close packing of oxygens in which the alternation of two kind of mixed layers containing Li and Ni in different ratios can be detected along the c direction. This model implies a Li order incompatible with the alternation of Ni layers, one of them pure and the other containing some Li. The results of magnetization measurements look consistent with the new structural type, and reveal that LixNi1−xO behaves as mictomagnetic.

We propose a new valence control method of codoping with doping Ga (or In, Al) donor and N acceptor at the same time for the fabrication of a low-resistivity p-type ZnO based upon the ab initio calculation. We compare our predicted materials design to fabricate a low resistivity p-type ZnO with the recent successful codoping. Based upon the success in the valence control of ZnO, we propose a materials design to fabricate the ferromagnetic Mn-doped p-type ZnO upon codoping. It is shown that the anti-ferromagnetic state is more stable than the ferromagnetic ones due to the anti-ferromagnetic super-exchange interaction, if we have no mobile holes. Upon codoping with the mobile holes, it is shown that the ferromagnetic state becomes more stable than the anti-ferromagnetic ones due to the ferromagnetic double-exchange interaction. However, it is shown that the anti-ferromagnetic state is more stable upon electron doping due to the anti-ferromagnetic super-exchange interaction. We calculate the chemical trends of the magnetic state in V-, Cr-, Fe-, Co-, and Ni-doped (25 at%) in ZnO, and predict that all of these materials show the ferromagnetic ground states without electron and hole doping.

La0.7Src.3MnO3 (LSMO) perovskite oxide films have been grown on (001) LaAlO3 (LAO) by pulsed laser deposition. The films were deposited in an ambient oxygen pressure of 0.1 m Torr to 200 mTorr and under different substrate temperatures. Their structural properties were examined by X-ray diffractometry. Heteroepitaxial growth was confirmed for films deposited at 650°C or above. Electrical measurements suggest that the charge carrier concentraticn of the films varies with their oxygen content and shows high stability against further thermal treatment. Semiconducting LSMO films at room temperature were obtained for deposition at oxygen pressure ≤ 60 m Torr. The epitaxial LSMO films have been used as the semiconducting channel of a ferroelectric field effect transistor. Heteroepitaxial Pb(Zr0.52Ti0.48)O3/LSMO/LAO structures have been fabricated and characterized.

A sequence of epitaxial La0.75Sr0.25MnO3 (LSMO) films with thickness ranging from 2400 to 50 Å have been prepared by pulsed laser deposition onto (110) SrTiO3 (STO) substrates. Compared with oar previous results on LSMO/STO(100) films [1], films on STO(110) substrates exhibit strong, anisotropy of electrical resistivity p. p measured in [110] direction is comparable with the resistivity of LSMO/STO(100) films while p in [001] direction is 25 times higher than in STO(100) case. The maximum value of anisotropy parameter p[001]/p[110] = 25 is reached for thick films at the low temperature of 90 K. Distinct crossover from 3D to 2D case has been observed. For thick films anisotropy monotonously decreases with the temperature increase. Films thinner than 200 Å exhibit a maximum of anisotropy parameter, which shifts to lower temperatures with the thickness decrease. The maximum temperature coefficient of resistivity (TCR) was found to be around 2% if measured along [001] direction and about 50 % higher in [11O] inplane direction. We explain the observed effects in terms of the crystalline properties of fabricated films.

We present experimental studies of crystalline, magnetic, and magneto-optic (MO) properties and their correlation with the processing parameters of Ce-substituted yttrium iron garnet (CexY3−xFe5O12) thin films grown epitaxially onto single crystal Gd3Ga5O12 (111) substrates by Nd:YAG pulsed laser deposition technique. Rutherford backscattering (RBS) analysis and microprobe energy dispersive spectrometry (EDS) prove the background oxygen pressure, used for films growth, control films stoichiometry. Oxygen ambient pressure appears to be an important parameter to grow CexY3−x, Fe5O12 films with good crystallinity, magnetic properties, as well as enhanced MO effect. It is found that the film fabricated at 50 mTorr oxygen pressure exhibits a maximum Faraday rotation (FR) øF = 1.78 deg/νtm at λ = 633 nm, a maximum saturation magnetization 4πMs = 1255 Gauss with a minimum in-plane coercivity Hc = 35 Oe, and the narrowest full width at half maximum FWHM = 0.06° of the (444) Bragg reflection rocking curve. The analog of the Verdet constant V = øF / 4πMs, also found to be dependent on the oxygen ambient pressure, reaches the value as high as 1.4 deg/νm-kG at 633 nm, suggesting that this material is useful for MO applications.

Electrical properties of Nb-doped SrTiO3 (STO:Nb) Schottky barrier (SB) junctions have been investigated in detail for a comprehensive understanding of metal/oxide interfaces. Using a high-purity ozone surface treatment, rectification ratio over 9th order of magnitude has been successfully obtained, while without the surface treatment, anomalous large reverse bias leak currents were observed in the current-voltage characteristic of the junctions. The X-ray photoelectron spectroscopy (XPS) shows that carbon contamination which adsorbed the STO:Nb surface in air, induces surface states in the band gap of the STO:Nb, which probably originate the large reverse bias leak currents of the metal/STO:Nb junctions. Thus we present importance, of surface treatment for oxides to obtain controllability and reproducibility of the electrical properties of the oxide devices. Photocapacitance spectroscopy has been performed to investigate deep levels due to bulk defects and impurities in the Au/STO:Nb junctions. The photocapacitance spectra clearly indicate existence of the deep levels in the Au/STO:Nb and the concentration of the deep levels were of the order of 1013∼1015 cm−3. These values are too low to affect the Fermi level pinning at the interface if the deep levels exist in the near surface region of the bulk STO:Nb. We have shown some interesting electrical properties, characteristic of the SB junction of the dielectric oxide compared with that of the conventional semiconductor's. The schematic band diagram of the Au/STO:Nb junction with the intrinsic low permittivity layer at the interface has been proposed, which explains all the characteristic electrical properties. Considering the chemical trend of the SB height (SBH) estimated from the J-V results, we have pointed out the importance of the metal reactivity for understanding the formation mechanism of the SBH.

Single phase Na0.5K0.5NbO3 (NKN) thin films have been pulsed laser deposited on SiO2/Si(C-01) wafers and LaAlO3(001) and MgO(001) single crystals. Radio frequency (up to 1 MHz) and microwave (up to 50 GHz) dielectric spectroscopy studies have been carried out to characterize thin NKN films for electrically tunable microwave device applications. Films on single crystal oxide substrates showed tunabilities as high as 30-40 % at 40 V bias and dissipation factor of 0.01-0.02 at 1 MHz. The films on Si substrates showed low dielectric losses of < 0.01, and low leakage currents. Dielectric properties of ferroelectric films on Si substrates at low frequencies are greatly influenced by the depletion capacitance and the resistance inserted by semiconductor substrate. Microwave frequency measurements for NKN film on Si wafers yield more than 10 % tunability at 50 GHz and loss tan σ <0.1 at 10 GHz.

Thin Ba0.2Sr0.8TiO3 films were pulsed laser deposited at laser pulse repetition rates of 1, 5 and 20 Hz in order to assess the effect of grain size on pyroelectric properties. Scanning electron microscopy reveals an increase in columnar grain size with decreasing laser pulse rate, as expected. Substrate bending measurements show an increase in tensile stress with increasing grain size, suggesting some form of stress relaxation has occurred. X-ray diffraction studies reveal all films to be epitaxial and oriented, while Rutherford Backscattering Spectroscopy finds no significant differences in film composition. The films grown at 5 and 20 Hz display a suppressed dielectric permittivity as a function of temperature, while the film deposited at 1 Hz displays an unusually sharp and large dielectric permittivity peak. A variation on current theory concerning phase transitions of stressed ferroelectric thin films is proposed to explain these results.

We have investigated the dielectric, insulating, structural, microstructural, interfacial, and surface morphological properties of Ba0.60Sr0.40TiO3 thin films Mg doped from 0 to 20 mol%. A strong correlation was observed between the films structural, dielectric and insulating properties as a function of Mg doping. Non textured polycrystalline films with a dense microstructure and abrupt film--Pt electrode interface were obtained after annealing at 750°C for 30 min. Single phase solid solution films were achieved at Mg doping levels up to 5 mol%, while multiphased films were obtained for Mg doping levels of 20 mol%. Decreases in the films dielectric constant, dielectric loss, tunability and leakage current characteristics were paralleled by a reduction in grain size as a function of increasing Mg dopant concentration. Our results suggest that Mg doping serves to limit grain growth and is thereby responsible for lowering the dielectric constant from 450 to 205. It is suggested that Mg behaves as an acceptor-type and is responsible for the doped films low dielectric loss and good leakage current characteristics. Performance-property trade-offs advocates the 5 mol% Mg doped Ba0.60Sr0.40TiO3 film to be an excellent choice for tunable microwave device applications.

An electrode plays an important role in realising a ferroelectric thin film as a potential memory device. We have investigated LaNiO3 (LNO) as a potential electrode material and evaluated the ferroelectric properties of oxide materials like strontium bismuth tantalate (SBT) and barium titanate(BT). We have successfully deposited epitaxial films of LNO on Pt coated Si(100) and LaAlO3 (LAO) substrates using the pulsed excimer laser deposition technique. We are able to grow high quality SBT and BT films on top of this LNO layer. The X-ray diffraction revealed the epitaxy of the LNO, SBT and BT films. The ferroelectric properties of SBTand BT were investigated using the RT66A ferroelectric tester.

High quality films of barium hexaferrite (BaFe12O19) were deposited by pulsed laser ablation onto MgO (111) substrates. In contrast to previous films deposited onto c-plane sapphire (Al203), these films were expected to have compressive biaxial stress, and indeed showed no indications for either cracking or delamination to a film thickness of 32 νm. All films were found to be highly c-axis textured by both x-ray diffraction measurements and magnetization results. The saturation magnetization (4πMs = 4.2 kG) and uniaxial anisotropy field (HA = 16 kOe) values for these films approach bulk values. Ferrimagnetic resonance measurements on a calcined 3 μm thick film show a narrow linewidth (ΔH ∼ 100 Oe) for the uniform resonance mode. The properties of these films approach those required for self-biased millimeter wavelength devices.

Epitaxial thin films of PbZr0.52Ti0.48O3 (PZT) have been synthesized successfully on SrRuO3/SrTiO3/MgO/TiN/Si heterostructures by pulsed laser deposition. The films were single phase and had (001) orientation. The deposition parameters were varied to obtain the best epitaxial layer for each of the compounds. Transmission electron microscopy indicated good epitaxy for the entire heterostructure and sharp interfaces between the epilayers. Dielectric and P-E hysteresis loop measurements were carried out with evaporated Ag electrodes. The dielectric constant for the films was found to be between 400-450. The value of saturation polarization Ps, was between 55-60 νC/cm2 and the coercive field Ec varied from 60-70 kV/cm. Integration of PZT films with silicon will be useful for future memory and micromechanical devices.

Sol gel solutions have been modified with hydrogen peroxide to improve the durability of photo-irradiated films to water and acidic solvents for photo-patterning. The solutions used for film fabricati.on are aqueous based and contain acetylacetonate (acac). UV-Vis absorption studies indicate that peroxide modifies the acetylacetonate ligand (in this case the zirconium precursor) creating a new absorbing species at longer wavelength which also affects the response of the acac ligand to UV radiation. Precursor modification and UV treatments have also been shown to impact the texture and improve the microstructure of resulting films. Depth profiling by radio-frequency glow discharge atomic emission spectroscopy indicates reduction in the carbon to hydrogen ratios of films crystallized after exposure to UV radiation.