Sarbani Basu

Planar Ultra-Wideband Bandpass Filter Using Edge Coupled Microstrip Lines and Stepped Impedance Open Stub

The design and implementation of a planar ultra-wideband (UWB) bandpass filter are presented. Three interdigital edge coupled microstrip lines are used for coupling enhancement. A stepped impedance open stub is used for realizing transmission zeros simultaneously in upper and lower stop bands as well as impedance matching in ultra-wide pass band. A pass band from 3.1-10.6 GHz is achieved with an insertion loss of 0.5 dB, a return loss of about 18 dB, a sharp out-of-band-rejection, and a low group delay of only 0.21ns. Single- and double-section filters are realized to meet the UWB mask requirement. The design of the filter is simple, and it shows good frequency response.

Miniature Dual-Band Filter Using Quarter Wavelength Stepped Impedance Resonators

A miniature dual-band filter using quarter wavelength (lambdag/4) stepped impedance resonators (SIRs) is proposed. Short and open SIRs are coupled together to realize lower and upper passbands, respectively. Miniaturization is achieved due to the use of lambdag/4 resonators and a combline coupling structure. Two transmission zeros in a mid-stopband and one in each lower and upper stopbands are achieved. In order to see the capability of this structure to achieve different second passband frequencies, two dual band filters at frequencies of 2.45/5.25 GHz and 2.45/5.75 GHz are realized. Measured insertion losses are 1.3 dB and 2.3 dB and return losses are better than 17 dB and 18 dB at the first and second passband frequencies, respectively, with a mid-stopband attenuation better than 30 dB. The size of the filter is as compact as 19.0 times 5.2 mm2 on a RO 4003C (epsivr = 3.38, h = 0.81 mm) substrate.

Liquid-phase deposition of Al2O3 thin films on GaN

Thin films of aluminum oxide (Al 2 O 3 ) on GaN substrates were grown by the process of low-temperature liquid-phase deposition (LPD), in which aluminum sulfate with crystallized water [Al 2 (SO 4 ) 3 .18H 2 O] and sodium bicarbonate [NaHCO 3 ] were used as the precursors. The pH value of the growth solution plays an important role in the deposition process. The best quality of the oxide thin film was obtained at the pH value of 3.80, while the growth rate was 35 nm/h at the optimized concentration values of Al 2 (S0 4 ) 3 = 0.0834 mol/L and NaHCO 3 = 0.211 mol/L and at the temperature of 30°C. The films were characterized by means of X-ray photoelectron spectroscopy, Auger electron spectroscopy, and atomic force microscopy. It was found that the leakage current density of 50 nm thin Al 2 O 3 oxide film was between 10 -4 and 10 -5 A/cm 2 at a negative electric field of 1 MV/cm, with the breakdown electric field being greater than 10 MV/cm. After annealing the oxide at 750°C for 30 min, the leakage current density was lowered to the value of 10 -6 -10 -7 A/cm 2 at the negative electric field of 1 MV/cm. The oxide-semiconductor interface state density as calculated from the capacitance-voltage curve was 3.89 X 10 11 cm -2 eV -1 .

Effects of Short-Term DC-Bias-Induced Stress on n-GaN/AlGaN/GaN MOSHEMTs With Liquid-Phase-Deposited

This paper presents a comparative study of the degradation of dc characteristics and drain current collapse under dc-bias stress in passivated metal-oxide-semiconductor high-electron mobility transistor (MOSHEMT), unpassivated HEMT, and passivated HEMT devices. The Al2O3 oxide thin film that is used as a gate dielectric and a passivation layer in MOSHEMTs is prepared by a simple, low-cost, and low-temperature liquid-phase deposition (LPD) technique. All devices are subjected to short-term dc-bias stress to investigate the reliability of the oxide and its passivation effect. In the case of MOSHEMTs and passivated HEMTs, the gradual reduction in drain current is found within 20-h drain-bias stress, which is apparently caused by the hot-electron injection and trapping in the buffer, and a barrier layer that is operated at a high drain voltage. However, faster degradation is found in unpassivated HEMTs, and some devices are permanently damaged due to the degradation of unpassivated surface states. Nonetheless, the current is partially recovered for all devices after gate stress, and no damage to the MOSHEMTs is observed. Therefore, it is believed that the Al2O3 thin film that is prepared through the LPD technique is effective as a gate dielectric and as a surface passivation layer in reducing device degradation during dc-bias stress and in diminishing the current collapse effect in MOSHEMTs.

\hbox{Al}_{2}\hbox{O}_{3}

Solution processible poly(4-vinylphenol) is employed as a transistor dielectric material for low cost processing on flexible substrates at low temperatures. A 6,13-bis (triisopropylsilylethynyl) (TIPS) pentacene-graphene hybrid semiconductor is drop cast to fabricate bottom-gate and bottom-contact field-effect transistor devices on flexible and glass substrates under an ambient air environment. A few layers of graphene flakes increase the area in the conduction channel, and form bridge connections between the crystalline regions of the semiconductor layer which can change the surface morphology of TIPS pentacene films. The TIPS pentacene-graphene hybrid semiconductor-based organic thin film transistors (OTFTs) cross-linked with a poly(4-vinylphenol) gate dielectric exhibit an effective field-effect mobility of 0.076 cm(2) V(-1) s(-1) and a threshold voltage of -0.7 V at V(gs) = -40 V. By contrast, typical TIPS pentacene shows four times lower mobility of 0.019 cm(2) V(-1) s(-1) and a threshold voltage of 5 V. The graphene/TIPS pentacene hybrids presented in this paper can enhance the electrical characteristics of OTFTs due to their high crystallinity, uniform large-grain distribution, and effective reduction of crystal misorientation of the organic semiconductor layer, as confirmed by x-ray diffraction spectroscopy, atomic force microscopy, and optical microscopy studies.

as a Gate Dielectric

A scheme for V-band band-pass filter (BPF) with narrowband performance and compact chip size is implemented using the 0.15 μm GaAs pHEMT process. Based on the even- and odd-mode analysis in V-band BPF, the feature of the third harmonic suppression can be concisely verified. The proposed structure provides excellent selectivity at both sides of the passband and facilitates the realization of third harmonic suppression of up to 20 dB. Good return loss and reasonable insertion loss over the desired passband are also shown.

Blending effect of 6,13-bis(triisopropylsilylethynyl) pentacene–graphene composite layers for flexible thin film transistors with a polymer gate dielectric

The performance of n-GaN/AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) with a 20 nm thick Al 2 O 3 gate oxide deposited using the low temperature liquid phase deposition technique is demonstrated. MOSHEMTs exhibit a 23% increase in saturation drain current density, 13% higher extrinsic transconductance, and a lower gate leakage current of 3 orders of magnitude in comparison with high electron mobility transistors. The stability and the interface quality of Al 2 O 3 /n-GaN by this alternative process are discussed. The sheet carrier concentration and Hall mobility are also estimated from the channel conductance under the gate, which is comparable with those measured by the van der Pauw method before the device processing.

MMIC Compact Filters With Third Harmonic Suppression for V-Band Applications

An integrated compact down-converter monolithic microwave integrated circuit chip is presented. It is designed using anti-parallel diode pair sub-harmonic image reject mixer and RF low noise amplifier. The quasi-lumped circuit components are employed in circuit design for the compact chip size. The conversion gain of the chip is 10-14 dB, image rejection above 20 dBc, and noise figure of 3.5-4.5 dB for the RF frequency of 29-36 GHz. The chip size is as compact as 2.24 mm2 on a 100 mum GaAs substrate thickness.

AlGaN/GaN Metal-Oxide-Semiconductor High Electron Mobility Transistor with Liquid Phase Deposited Al2O3 as Gate Dielectric

AlGaAs/InGaAs/GaAs metal-oxide-semiconductor–pseudomorphic high electron mobility transistors (MOS-PHEMTs) with Al2O3 as a gate dielectric oxide prepared in low-temperature liquid phase deposition (LPD) are presented in this study. The Al2O3 films on the GaAs substrates are characterized by means of x-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy. The applications to depletion mode n-channel GaAs MOS-PHEMTs showed larger gate swing voltage, lower gate leakage current, higher breakdown voltage, higher drain current density, and maximum extrinsic transconductance compared to conventional AlGaAs/InGaAs PHEMTs. This demonstrates that LPD Al2O3 could be a suitable candidate for future gate insulator applications.

Highly Integrated Ka-Band Sub-Harmonic Image-Reject Down-Converter MMIC

The integrated MMIC chips for Ka-band transceiver applications are reported. The reported transceiver chips are the compact integrated wideband upconverter, miniature size integrated upconverter, integrated downconverter, two-stage (0.8 W) and fourstage (1.9 W) power amplifiers. The compact wideband integrated upconverter chip (4.2 mm2) is provided conversion gain of 10-15 dB and sideband suppression above 20 dBc over 23-37 GHz with required LO power between 9-16 dBm. The miniature upconverter chip (2.4 mm2) is achieved the gain of 10-13 dB and sideband suppression above 20 dBc over 27-38 GHz at LO power of 0 dBm. The integrated downconverter chip (2.4 mm2) is measured with conversion gain of 1014 dB, image rejection above 20 dB, and noise figure of 3.5-4.5 dB over 29-35 GHz for LO power between 911 dBm. The two-stage power amplifier is shown the measured small signal gain above 12 dB over 31-36 GHz and saturated power of 0.8 W at 31 GHz. The four-stage power amplifier chip is measured with small signal gain of 20-25 dB over 25-30 GHz and saturated power of 1.9 W at 27 GHz.