NISCAIR Online Periodicals Repository Collection: IJPAP Vol.50(03) [March 2012]

Fabrication of ISFET microsensor by diffusion-based Al gate NMOS process and determination of its pH sensitivity from transfer characteristics

Title: Fabrication of ISFET microsensor by diffusion-based Al gate NMOS process and determination of its pH sensitivity from transfer characteristics

Authors: Khanna, V K

Abstract: The present paper describes the fabrication of ISFET (Ion-Sensitive Field-Effect Transistor) by a four-mask, thermal diffusion-based process. The sequence of physical and chemical processes for ISFET fabrication has been elaborated. In the first photomasking step, the regions for source and drain diffusion have been opened. The second photolithography defined the gate area. In the third photolithographic step, contact windows have been opened, and in the fourth photolithographic step, the metal pattern has been delineated. After completion of the fabrication process, the wafer has been diced into chips, which have been mounted on ceramic substrates to provide electrical connections for source, drain and substrate. Except for the gate region, the whole chip and wire bonds have been protected with insulating epoxy. For process characterization, current-voltage characteristics of MOSFET test devices simultaneously fabricated on the same wafer have been measured for gate-source voltages from –5 to +5 V. These were found to be N-channel, depletion-mode devices indicating similar behaviour for ISFETs. The pH-response of ISFET has been evaluated by drawing its I_DS-V_GS characteristics after immersion in standard buffer solutions and applying the gate-source voltage through Ag/AgCl reference electrode. From these transfer characteristics, pH-sensitivity of ISFET has been determined by finding the gate-source voltage necessary to ensure constant I_DS, V_DS condition. Technological shortcomings of this work have also been pointed out, and necessary remedial measures have been suggested.

Page(s): 199-207

Versatile current-mode universal biquadratic filter using plus-type dual-output ICCIIs

Title: Versatile current-mode universal biquadratic filter using plus-type dual-output ICCIIs

Authors: Chen, Hua-Pin

Abstract: In this paper, a versatile three-input and three-output universal current-mode biquadratic filter is proposed. The circuit employs three plus-type dual-output inverting second-generation current conveyors (DO-ICCIIs) as active elements together with three grounded resistors and two grounded capacitors. The proposed configuration exhibits high-output impedance which is important for easy cascading in the current-mode operations. It can be used as either a single-input three-output or three-input two-output circuit. In the operation of single-input and three-output circuit, the lowpass, bandpass and bandreject can be realized simultaneously while the highpass filtering response can be easily obtained by connecting appropriate output current directly without using additional stages. In the operation of three-input and two-output circuit, all five generic filtering functions can be easily realized by selecting different three input current signals. The filter permits orthogonal controllability of the quality factor and resonance angular frequency and no component matching conditions or inverting-type input current signals are imposed. All the passive and active sensitivities are low. Post-layout simulations are based on using TSMC 0.18μm 1P6M CMOS process technology and supply voltages ±0.9V to verify the theoretical analysis.

Page(s): 188-198

Modification and designing of electrodeposited polypyrrole film for optoelectronic applications

Title: Modification and designing of electrodeposited polypyrrole film for optoelectronic applications

Authors: Sharma, I D; Sharma, V K; Dhawan, S K; Saini, P K

Abstract: The electrodeposited polypyrrole (PPY) film over ITO coated glass substrate has been prepared and its current voltage response using Schottky emission theory has been analyzed. The electrodeposition of PPY has ben carried out by electrochemical polymerization of 0.2 M pyrrole monomer and cycling the potential between -0.2V to 0.8 V at a scan rate of 20mV/s using KCl as supporting electrolyte. The formation of polymer has been confirmed by X-ray diffraction and FTIR measurements whereas the surface morphology has been observed using scanning electron microscope. The band gap of PPY film has been calculated using UV visible spectroscopy and found to be 2.4 eV. In addition, the current-voltage response of deposited film was also recorded to evaluate its electronic attributes such as barrier height (Ø_B) and constant factor (β). The results revealed the Ø_Band β values of 0.314 eV and 1.72´10^-4, respectively. These films may have potential applications in electronic and optoelectronic sensing devices.

Page(s): 184-187

Dielectric behaviour of aprotic polar liquid dissolved in non-polar solvent under static and high frequency electric field

Title: Dielectric behaviour of aprotic polar liquid dissolved in non-polar solvent under static and high frequency electric field

Authors: Sahoo, S; Middya, T R; Sit, S K

Abstract: Dielectric behaviour of aprotic polar liquids (j) like N,N dimethylformamide (DMF), N,N dimethylacetamide (DMA) and acetone (Ac) has been studied under static as well as 9.987, 9.88 and 9.174 GHz electric field employing Debye theory of polar-non polar liquid mixture in terms of measured ε'_ij and imaginary ε"_ij part of complex relative permittivity ε_ij*, static ε_0ij and high frequency ε_∞ij for different w_j’s of solute dissolved in non polar solvent at 27°C temperature. Double relaxation times τ₂ and τ₁ due to whole molecule and part of the polar molecule have also been estimated analytically using the complex high frequency orientational susceptibility _ij* (= ε_ij*-ε_∞ij) from measured data for DMF and DMA in C₆H₆ and CCl₄ as well as acetone in C₆H₆ and CCl₄ solvent, respectively at 27°C. Out of the six systems, three systems show double relaxation time τ₂ and τ₁ and dipole moment μ₂ and μ₁. The estimated μ’s and τ’s agree excellently well with the reported and measured values from ratio of slope and linear slope method. The dipole moments μ_0s’s in static electric field are also compared with μ_j’s in hf method. The relative contributions c₁ and c₂ due to τ₁ and τ₂ have been calculated from Fröhlich equation as well as graphical plot of '_ij/_0ij -w_j and ''_ij/_0ij -w_j curve at w_j→0. Solute-solute and solute-solvent molecular associations are ascertained in different molecular environment.

Page(s): 175-183