A lateral DMOS merged bipolar transistor, LDBIMOST, in Darlington/parallel combinations has been fabricated using a high resistivity p-substrate to handle large currents with superior speed. LDBIMOST has the same structure as a lateral double-diffused MOS transistor (LDMOST) with p-body as a base of an active npn bipolar transistor. The device has been modelled using process and device computer programs and a circuit simulator to optimize the design to obtain a high breakdown voltage, low Ron and parasitic-free monolithic merged LDMOS bipolar structure. The influence of gate potential and gate metal over the drift-region on Ron has been investigated. Several LDMOS test structures with varying channel width have been designed to study electrical performance. It has been revealed that an additional integration of LDMOST along with an LDBIMOS transistor on the same chip with the minimum area concept has improved the turn-off speed of the device from 490 ns to 270 ns at a current level of 1.3 Amp

A FET-ammonia sensor operating at room temperature is reported in this paper. The sensor employs a thin film of semiconducting Y:Ba:Cu:O (YBCO) compound, commonly known as 1-2-3 high temperature superconducting cuprate, as its sensing element. We observed that this material is highly and selectively sensitive to ammonia at and below room temperature. The measurements indicate that the non-amplified signal of the sensor is more than 10 mV for 5 ppm of ammonia. A typical rise time of 24 s and fall time of 250 s is measured at room temperature. The measurements on temperature dependence of sensitivity evince that the sensor signal increases if the operating temperature of the sensor is decreased. The sensor is selectively sensitive to ammonia only and exhibits a non-sensor like behaviour to hydrogen and hydrocarbon based gases. Although the exact mechanisms of gas-sensing properties of cuprates are not known, nevertheless, we tried to explain the observed sensor response to ammonia on the basis of physisorption. The demonstrative results reported here suggest that a room temperature FET ammonia sensor can be realized using semiconducting YBCO as a sensing material for the development of silicon-based integrated smart sensors.

Silicon nitride deposition by chemical vapour deposition (CVD) based techniques like low pressure CVD (LPCVD) and plasma enhanced GVD (PECVD) is described in this paper. The technological advantages of silicon nitride deposition by these two techniques, developed at CEERI, are discussed in detail. Applications of LPCVD nitride films for LOGOS, composite gate structures for MNOS and MOS devices are highlighted. The importance of PECVD nitride films for diffusion masking of compound semiconductors, and for passivation in Si, GaAs, and InP devices are demonstrated. Process parameters of LPCVD and PECVD nitride deposition have been optimized for various substrate conditions depending on the technological requirements. Material properties are being explored for various micromachining activities, which includes diaphragm, cantilever, and beam formations.

s ili con based FET -sensors. However, an appropriate passivation is needed for their incorporation in s ilicon-CMOS technology. Utilization of thin gold films for thi s purpose is reported he re for th e gas sensing properties of gold-coated YBCO films. RF magnetron sputtering is used to deposit YBCO films on oxidized si li con substrates. These films are then coated with a thin gold layer and used to construct discrete structures of capacitively controlled field effect trans istor (CCFET) sensors to investigate their gas detection properties. The measurement technique and sensor response are discussed in detail. The result s evince th at gold-coated YBCO film s are sensitive to ammonia at room temperature and can be employed as sensitive layer in integrated silicon-FET sensors for detection of ammonia.

Cobalt oxide has been reported as a new material for room temperature FET gas sensor. Thin films of cobalt oxide have been prepared by DC magnetron sputtering on oxidized silicon substrates and used as gas sensitive layers in a capacitively controlled field effect transistor (CCFET) structures. CCFET is a MOSFET with an extended gate electrode. Gas sensing behaviour of these films has been investigated at room temperature for different gases of varying concentrations, ranging from 10 ppm to 10,000 ppm. Gases such as CH4, C3H8, NH3, CO, NO and H-2 have been used to study the sensor performance. Since the measured sensor signal is not amplified, it is a direct measure of sensitivity of the film to a gas to which it is exposed. The CCFET structure, preparation of sensitive films and measurements are described in this paper. The results indicate that cobalt oxide is selectively sensitive to ammonia and hydrocarbon gases only with a little or negligible response to other gases. Signals of 5 mV and 30 mV for 10 ppm of the hydrocarbons and ammonia, respectively have been observed.

We have discovered an interesting property of high Tc cuprates, which are popularly known as high temperature superconductors, for gas sensing applications. Metallic films of YBCO and BSCCO compounds are examined for gas-sensing properties by incorporating them in a FET-sensor structure. These multi-component ceramic oxides exhibited room temperature gas detection capability in comparison to conventional metal-oxides, which are sensitive to gases only at elevated temperatures. The sensor responses to NH3, H2, CO, CO2, NO, NO2, and hydrocarbon gases are presented and discussed. The results evince that thin film of high Tc cuprates are highly sensitive to NH3 and NO2 at and around room temperature and less sensitive to other gases. These films, therefore, can be used to realize a room temperature low power FET-gas sensor.

We report a new FET sensor which can detect ammonia at room temperature. We discovered a new application of high T/sub c/ cuprates, commonly known as high temperature superconducting copper oxides. The gas sensing properties of thin films of these materials have been examined through work function measurements. Thin films of YBCO and BSCCO are prepared on oxidized silicon substrates. These are then used in a capacitively controlled field effect transistor. One plate of the capacitor is a gas sensitive film and the other one is a reference electrode which is connected to the FET gate electrode. The operating principle of this sensor is based on the change in work function of the sensitive film due to gas adsorption on its surface. This is measured as change in transistor gate voltage. Measurements show that the nonamplified sensor signal is more than 10 mV for only 5 ppm of ammonia. Typical rise time of 24 sec and fall time of 250 sec are measured at 18°C. The sensor is selectively sensitive to ammonia and shows little or no response to hydrogen and hydrocarbon based gases. Measurements at different temperatures reveal that the sensor performs optimally in the 15-25°C temperature range. Device sensitivity to carbon monoxide, carbon dioxide, hydrogen and hydrogen gases has been found to be negligibly low. Thus a new FET sensor capable of sensing ammonia with selectivity around room temperature is reported in this paper.

The wet chemical treatment using SeS2 is an inexpensive and simple method of depositing selenium on GaAs surfaces. This treatment improves the electronic properties of the surface as seen from the increase in photoluminescence intensity. We present our results on surface structural investigations of GaAs(110) surface passivated by SeS2 treatment using atomic force microscopy. Our results show that SeS2 treatment can passivate the GaAs(110) surface forming ordered overlayers on it.

The phenomenon of resist debris (RD) formation in electron beam lithography (EBL) under various conditions of proximity exposure (PE) effect is discussed. It is found that the PE correction at the preferred resist plane together with adequate beam to beam spacing can provide stable and uniformly distributed RD over the exposed pattern area. As an application of such stable and uniformly distributed RD, the fabrication of an array of closely spaced metal dots has been demonstrated. The approach provides the optimum way for achieving high resolution pattern delineation under the given EBL conditions and constraints.

Surface structure studies of GaAs(100) with and without chemical passivation have been made using atomic force microscopy (AFM). Passivation was carried out using a solution of SeS2 which has proved to be a successful passivating agent as seen from the increase in the photoluminescence (PL) intensity. Atomic force microscopy results indicate that it is possible to obtain ordered surface layers on GaAs using SeS2.

The interface between silicon (100) and thermal silicon dioxide grown by wet, dry, and trichloroethylene oxidation has been investigated by scanning tunneling microscopy and scanning tunneling spectroscopy. The scanning tunneling microscopy images of the silicon surface, after removal of oxide, reveal the presence of silicon bumps (protrusions) in samples prepared by wet and dry oxidation while no protrusions are seen at the interface of trichloroethylene oxidized samples. The spectroscopic measurements predict that these are silicon protrusions and are produced by oxide growth conditions. X-ray photon spectroscopy on samples containing protrusions also supports the above prediction. Thus, our study suggests that roughness of the silicon–silicon dioxide interface depends on oxide growth conditions and a relatively smooth interface is obtained by tricholoroethylene oxidation.

Surface topography of as-grown films of YBa2Cu3O7-delta (YBCO) deposited by off-axis RF magnetron sputtering on MgO and SrTiO3 single-crystal (100) substrates, has been investigated by scanning tunnelling microscopy (STM)/scanning tunnelling spectroscopy (STS) operated in air at ambient temperature. Both c-axis- and a-axis-oriented YBCO films have been investigated. In the case of c axis thin films, we have directly observed spiral-shaped growth terraces, which emanate from screw dislocations of this layered superconducting oxide. The growth steps are generally seen to possess a step height close to or multiples of the unit cell height of the YBCO crystalline structure. In the case of a axis growth, the substrate as well as the deposition temperature determines the grain orientation. Furthermore, our STS data revealed that the surface layer of the film is semiconducting and the tunnelling spectrum varies its shape depending on the tip-to-sample distance. A superconducting gap appears clearly in the spectra when the STM tip is placed closer to the surface than the normal position of the scanning mode. This suggests that the semiconducting layer is confined in the topmost surface region of the as-prepared film, while the layer beneath it is superconducting in character.

Zinc sulphide nanoparticles in the size range similar to 10-40 Angstrom diameter have been synthesized using the aqueous chemical method. Scanning tunneling microscopy showed that particles are indeed nanosize particles. The size dependent band gap could be varied from a bulk value of 3.68 to 4.5 eV. X-ray diffraction indicated that nanoparticles are crystalline except for those with band gap similar to 4.5 +/- 0.1 eV. Nanoparticles with particle size similar to 21 X 2 Angstrom diameter or energy gap 4.1 X 0.1 eV were doped with manganese. The photoluminescence peak at similar to 600 nm corresponding to yellow light emission was observed. Atomic absorption studies show that maximum luminescence intensity is achievable with 0.12 at. wt% of Mn doping. (C) 1995 American Institute of Physics.

Effects arising from the intercalation of excess oxygen in Bi–O layer has been observed at room temperature using atomic force microscopy. The excess oxygen is incorporated by oxygenating the pure sample. The oxygen is trapped between the alternating Bi–O layers along the b direction. This leads to a change in the local interatomic bond length along the b axis, while the periodicity remained invariant along the a axis. In addition, in-plane atomically resolved structure of single crystal has been imaged at room temperature using AFM. The lattice spacings indicate that the observed structure corresponds to the in-plane bismuth and oxygen positions. Furthermore, high-resolution scanning tunneling spectroscopy measurements show that oxygen doping increases the Bi–O layer density of states near the Fermi level giving rise to metallicity, whereas the pure sample reveals a semiconducting energy gap in the tunneling spectrum.

In this article, recent results employing scanning tunneling microscopy-based techniques for the generation of nanometer-scale patterns on hydrofluoric acid treated silicon(100) and YBa2Cu3Ox superconducting thin films are presented. Furthermore, we were able to extract silicon (Si) atoms from Si(100)−1×1 surfaces, thereby producing silicon vacancies in the surface. These results thus demonstrate a possible approach for the construction of an atomic scale data memory as well as fabrication of artificial nucleation sites. The emission mechanism is believed to be field assisted evaporation due to the close proximity of the surface and the probe of the microscope.

Filling via-holes with metal films is one of the most important processes for the development of a multi-level metallisation system. By employing rf bias sputtering, vias of different feature sizes were filled with AlSi films. The process of via-hole filling and the effect of substrate voltage is described. The surface topography and cross section of the filled via-holes are shown. A two-level metal interconnection structure using sputtered AlSi was fabricated. The structure was characterised for the intra-level and inter-level shorts and the continuity of via chains. The process is described and the results are presented.

Darlington and parallel operations have been monolithically integrated using DMOS technology to develop a BiMOS transistor chip for superior switching speed with high current and power handling capacity for digital/analog circuitry. To achieve higher switching speed, an additional MOSFET has been integrated on the same chip and the switching time of the BiMOS transistor has been reduced to 240 ns at a collector current of 1 A. A CAD (computer-aided design) analysis has been performed using a device and circuit program to determine the interdependence of gain, transconductance, and threshold voltage with regard to channel length, base charge, oxide charge and thickness and ratio of channel width to length. To control VT, a cleaning procedure has been developed, and it is observed that IPA rinsing results in a low C-V shift of only 33 mv, a trap charge density of 4×1010 cm2/eV, and a high dielectric strength of 8 to 12 MV/Cm

UV-curable tetra-functional epoxy acrylate (EA4) was newly synthesized using 4,4′-methylenebis(N,N-diglycidylaniline). Effects of reaction temperature and epoxy/acrylic acid molar ratios on the reaction conversion were investigated. The conversion of epoxy to ester group was monitored by FTIR spectroscopy and the relative concentration of epoxy value and conversion of the reactions were calculated from FTIR data, in different intervals of the reaction time. EA4 curing under UV irradiation was studied, and the physicochemical characteristic of the cured resin was determined. DMTA, TGA and mechanical properties of the casted films were evaluated. Moreover, studies on effect of the synthesized EA4 content on properties of conventional epoxy acrylate (EA2) were carried out. According to TGA and DMTA studies, the UV-cured blend films of EA2 containing ≤9% EA4 presented film homogeneity, and improved thermal and mechanical properties. Thus, it can be used as a crosslinking agent in UV-curable formulations.

Investigations are made on contact and interconnect properties for scaling MOS transistor technology employing sputtered TiSi2 metallization. The contact resistance of different contacts varying in size is measured for n+ SiTiSi2 shallow junction contacts using Kelvin test structures. It is found that the contact resistance almost doubles when the contact size is reduced from 5 to 2 microns. The results are compared with the conventional AlSi 2% contact metallization. The electrical and structural properties of n+ poly SiTiSi2 composite structures are studied as gate and interconnect metallization. The optimum conditions for doping thin poly-Si without affecting thin gate dielectric properties is given. The sheet resistance for the polycide structures is reduced to 2 ohm sq−1 from 40 ohm sq−1 for poly-Si structures for gate metallization. The thermal ability of structures is also examined and the results are discussed.

An extremely reliable tungsten silicide is formed by reacting tungsten film with silicon wafer. The tungsten film is RF magnetron sputter-deposited onto a silicon wafer and is subjected to a novel discharge treatment. As a result, an amorphous tungsten silicide is induced. Finally, an effective tungsten silicide with tetragonal end phase and low sheet resistance forms when the sample is suitably vacuum-annealed at high temperature.