S. Halder

Lehigh University, Bethlehem, PA, United States

Are you S. Halder?

Claim your profile

Publications (41)26.22 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Closed-loop control of microelectromechanical systems (MEMS) capacitive switches was demonstrated by using an intelligent CMOS circuit. The control was based on fine tuning the bias magnitude of the switches according to the difference between sensed and targeted capacitances. Innovative designs were used to allow the CMOS circuit to sense low capacitance and to handle high voltage. The CMOS die of 3 × 1.5 mm2 was dominated by input/output and voltage regulation/protection circuits; the actual capacitance sense/control circuit was smaller than 0.1 mm . The entire circuit consumed 0.7 mW of power during active sense/control, which could be significantly reduced with less frequent sense/control and advanced CMOS technology. With a maximum actuation voltage of ±40 V and a target capacitance of 0.5 pF, a control accuracy of ±2.5% was demonstrated, which could be improved to ±1% with reduced parasitics through monolithic integration. Intelligence was programmed to alternate the bias sign when its magnitude required to maintain the targeted capacitance drifted significantly due to charging of the switch dielectric. Such intelligent control could also be used to compensate for process variation, material creep, ambient temperature change, and RF power loading, which would make MEMS capacitive switches not only more reliable, but also more robust.
    IEEE Transactions on Microwave Theory and Techniques 01/2013; 61(1):464-471. · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A CMOS control circuit capable of closed-loop capacitance sensing and control of RF MEMS switches was designed, fabricated, and tested. The control was based on fine-tuning the magnitude of the bias voltage of the switches according to the difference between sensed and targeted capacitances. Intelligence could be programmed by periodically alternating the sign of the bias voltage when its magnitude to maintain the targeted capacitance drifted significantly due to dielectric charging. Such an intelligent control could also be used to compensate for process variation, ambient temperature change, and RF power loading, which would make RF MEMS capacitive switches not only more reliable, but also more robust.
    Microwave Symposium Digest (MTT), 2012 IEEE MTT-S International; 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: RF power-handling capacity of micro-electromechanical capacitive switches was modeled by multiphysics finite-element analysis. Coupled electromechanical, electrothermal and thermomechanical models were constructed by using commercially available software. Simulations by using the models were validated by small- and large-signal RF measurements. The measurements showed that the power-handling capacity of the switches depended on not only the properties of the membrane (the movable part of the switches), but also the substrate properties and the circuit environment. These effects were captured in a compacted model, which could be used to guide the improvement of the power-handling capacity of the switches.
    Solid-State Electronics 12/2011; 65-66:219-225. · 1.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic layer deposition (ALD) Al2O3 film as a gate dielectric and for surface passivation simultaneously. Compared to the conventional AlGaN/GaN HEMT of the same design, six order of magnitude smaller gate leakage current and tripled drain current at forward gate bias demonstrate the effectiveness of ALD Al2O3 as a gate dielectric. The high transconductance and high effective two-dimensional electron mobility verify the high-quality of Al2O3/AlGaN interface with low interface trap density. The Al2O3 passivation effect is also studied by sheet resistance measurement and short pulse drain characterization.
    International Journal of High Speed Electronics and Systems 11/2011; 14(03).
  • [Show abstract] [Hide abstract]
    ABSTRACT: Compact measurement setup and test structure for nanosecond electroporation of biological cells were demonstrated. The test structure was based on a coplanar waveguide with a defected ground structure that afforded broadband impedance match with little dispersion or parasitic. The defected ground structure with a 10-μm gap formed a microchamber to readily accept biological solutions and to allow the measurement to be quickly performed before the solution evaporated or the cell activity changed. The measured results in conjunction with detailed electromagnetic analysis of a three-layer spherical cell model showed that the present measurement setup was capable of delivering a nanosecond 0.1-V potential across a plasmatic membrane. This transmembrane potential, although an order of magnitude lower than the typical threshold for membrane poration, could be increased by using nanosecond pulses with order-of-magnitude higher amplitude or 10-ns pulses with three times higher amplitude.
    Microwave Symposium Digest (MTT), 2011 IEEE MTT-S International; 07/2011
  • Xi Luo, Subrata Halder, James C.M. Hwang
    [Show abstract] [Hide abstract]
    ABSTRACT: form only given, as follows. The ruggedness of HBT Class-C power amplifiers was improved by adding an anti-parallel diode to the amplifier input to limit the negative swing of the base-emitter voltage. The improved amplifier could withstand 3∶1 instead of 2∶1 mismatch in CW operation, and 2.5∶1 instead of 1.5:1 mismatch in pulse operation. The present approach is simple to implement and has negligible impact on overall amplifier output power, gain or efficiency.
    IEEE MTT-S International Microwave Symposium digest. IEEE MTT-S International Microwave Symposium 06/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: form only given, as follows. RF power, when approaching the handling capacity of microelectromechanical capacitive switches, was found to accelerate both the charging and discharging of the dielectric in the switches. The amount of acceleration appeared to be greater than what could be explained by self biasing and self heating. Since the long-term reliability of the switches is limited by dielectric charging, the RF power-handling capacity of the switches may have to be derated to ensure long-term reliability.
    IEEE MTT-S International Microwave Symposium digest. IEEE MTT-S International Microwave Symposium 01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Using a novel sub-nanosecond pulse current-voltage measurement technique, InGaP/GaAs heterojunction bipolar transistors (HBTs) were shown to survive strong impact ionization and to have a much larger safe operating area (SOA) than previously measured or predicted. As the result, an empirical model for impact ionization with both voltage and current dependence was extracted and added to a commercially available HBT model. The modified model could predict the HBT characteristics across the enlarged SOA, as well as the performance of ultra-wideband pulse generators and the ruggedness of continuous wave Class-C power amplifiers.
    IEEE Transactions on Microwave Theory and Techniques 01/2011; · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An ultra-wideband pulse generator was designed and fabricated in GaAs HBT IC technology. The generator includes delay and differential circuits to convert a TTL input into a Gaussian pulse signal as well as a Class-C amplifier to boost the pulse amplitude while compressing the pulse width. By adjusting the collector bias of the Class-C amplifier, the pulse amplitude can be varied linearly between 3.5 V and 11.5 V while maintaining the pulse width at 0.3 ± 0.1 nanosecond. Alternatively, by adjusting the base bias of the Class-C amplifier, the pulse width can be varied linearly between 0.25 ns and 0.65 ns while maintaining the pulse amplitude at 10 ± 1 V. Finally, the amplified Gaussian signal can be shaped into a monocycle signal by an L-C derivative circuit. The present pulse generator compares favorably with pulse generators fabricated in CMOS ICs, step-recovery diodes, or other discrete devices.
    Active and Passive Electronic Components 01/2011; 2011.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Small- and large-signal RF characteristics were measured on AlN/GaN HEMTs with 80-160 nm gate length and 100-300 μm gate width. Consistent with the literature, current-gain cut-off frequency and maximum frequency of oscillation were found to increase with inverse gate length independent of gate width. For the first time, output power and efficiency were reported at the high end of X-band, and were comparable to the best reported at 2 GHz, consistent with that estimated from DC characteristics, and insensitive to gate length or width. These results suggest that the performance of AlN/GaN HEMTs is quickly catching up with that of the more mature AlGaN/GaN HEMTs and may be scaled to even higher frequency and higher power.
    Radio-Frequency Integration Technology (RFIT), 2011 IEEE International Symposium on; 01/2011
  • Subrata Halder, James C. M. Hwang
    [Show abstract] [Hide abstract]
    ABSTRACT: The lossy cable in a conventional load-pull setup was replaced with an active fixture to realize full tuning range by using passive electromechanical tuners. The approach was validated in small-signal characterization of a through line up to the edge of the Smith chart, as well as large-signal characterization of a heterojunction bipolar transistor up to a voltage standing-wave ratio of 10:1. The approach is simpler than active load-pull setups and it significantly enhances the capabilities of conventional load-pull setups, especially in the characterization of high-power transistors with very low matching impedances.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A robust design of RF MEMS capacitive shunt switches was implemented with a movable gold membrane, separate and non-contacting actuation pads, and electrostatic actuation. The same design was fabricated on silicon and quartz substrates with different combinations of dielectric constant, resistivity, thermal conductivity, and thermal expansion coefficient. It was found that most switches could operate between 0°C and 60°C and handle hot switching up to at least 5.6 W. However, the pull-in voltage of the switches fabricated on quartz had stronger temperature and power dependence than that on silicon. This was attributed to greater thermal expansion mismatch, impedance mismatch and self-heating on quartz. These results show that the power-handling capacity of a switch is determined by not only its membrane design, but also its circuit environment.
    Microwave Conference (EuMC), 2010 European; 10/2010
  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel technique is proposed for determining the actual pixel size in dense arrays of infrared detectors. The technique is based on probing individual pixels in an array and analyzing the parasitic bipolar transistor formed between them to determine the lateral diffusion width and, hence, the actual pixel diameter. The actual pixel diameter can then be used to separate the area-dependent dark current from the periphery-dependent dark current. The result shows that, in the present arrays, the dark current is dominated by the periphery current, unless the pixels are so close to each other that their depletion regions overlap.
    IEEE Electron Device Letters 08/2010; 31(8):839-841. · 2.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Last year, we reported on a SPICE-based compact RF small-signal electromechanical model for electrostatically actuated MEMS capacitive shunt switches with movable membranes. We now report on the enhancement of the model to include electrothermal and thermomechanical effects so that the model is applicable under large-signal RF conditions. Specifically, a thermal subcircuit is added to account for the temperature rise in the switch membrane as a function of the dissipated RF power. In turn, the temperature rise is used to evaluate the decrease in the membrane spring constant. These enhancements allow the present multiphysics model to simulate the coupled self-biasing and self-heating effects under RF large signals and to predict the power-handling capacity of MEMS capacitive switches. Additionally, the model has been coded in Verilog, making it portable between different circuit simulation environments.
    Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International; 06/2010
  • [Show abstract] [Hide abstract]
    ABSTRACT: Using a novel sub-nanosecond pulse current-voltage measurement technique, InGaP/GaAs heterojunction bipolar transistors were shown to survive strong impact ionization and to have a much larger safe operating area than previously measured or predicted. As the result, an empirical model for impact ionization was constructed and added to a commercially available HBT model. The modified model can predict the HBT characteristics across the enlarged safe operating area, including strong avalanche breakdown and flyback. The modified model can be used to simulate not only the ruggedness of high-power amplifiers, but also the performance of ultra-wideband pulse generators.
    Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International; 06/2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: For the first time, an ultra-wideband pulse generator is fabricated in GaAs HBT IC technology. The generator includes delay and differential circuits to convert a TTL input into an impulse signal and a Class-C amplifier to increase the pulse amplitude while compressing the pulse width. By adjusting the bias of the Class-C amplifier, the pulse amplitude can be varied linearly between 3.5 V and 11.5 V while maintaining the pulse width at 0.3±0.1 ns. Alternatively, the pulse width can be varied linearly between 0.25 ns and 0.65 ns, while maintaining the pulse amplitude at 10±1 V. Finally, the amplified impulse signal can be shaped into a monocycle signal by an L-C derivative circuit. These results compare well with that of pulse generators fabricated in GaAs HEMT, Si CMOS or Si discrete technologies.
    Microwave Conference, 2009. APMC 2009. Asia Pacific; 01/2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper compares the characteristics of an RF microelectromechanical systems (MEMS) capacitive switch with a molybdenum membrane versus that of a switch with similar construction but with an aluminum membrane. In comparison, the molybdenum switch exhibits a significantly reduced sensitivity to ambient temperature change so that its pull-in voltage varies by less than 0.035 V/??C. In addition, large-signal RF performance of the switches was compared under both continuous wave and pulse conditions. The results show that under large RF signals, the self-biasing effect is exacerbated by the self-heating effect and the self-heating effect is in turn amplified by nonuniform current and temperature distributions on the membrane. Measurements of both molybdenum and aluminum switches demonstrate a hot-switched power-handling capacity of approximately 600 mW. Since aluminum has been used as a membrane material for over a decade while molybdenum is new, the above results indicate that molybdenum is a promising membrane material for RF MEMS capacitive switches.
    IEEE Transactions on Microwave Theory and Techniques 01/2010; · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Using a novel sub-nanosecond pulse current-voltage measurement technique, InGaP/GaAs heterojunction bipolar transistors were shown to survive strong impact ionization and to have a much larger safe operating area than previously measured or predicted. As the result, an empirical model for impact ionization was constructed and added to a commercially available HBT model. The modified model can predict the HBT characteristics across the entire safe operating area, including strong impact ionization and flyback. The modified model can be used to simulate not only the ruggedness of power amplifiers, but also the performance of impulse-based ultra wideband pulse generators.
    01/2010;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Self heating in electrostatically actuated RF MEM capacitive shunt switches is analyzed by coupled electrical and thermal simulations using three-dimensional finite-element analysis. The result shows that despite highly nonuniform current and temperature distributions, the self-heating effect can be approximated by lumped thermal resistances of the switch membrane and the substrate. Additionally, since the thermal resistance of thermally insulating substrates such as quartz is significant compared to that of the membrane, it is important to consider the heat transfer across both the membrane and the substrate.
    01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Shifts in the pull-in voltage of electrostatically actuated MEMS capacitive switches were characterized under pulse RF excitation, which allowed the electrical and thermal effects of the RF excitation to be separated. The resulted multi-physics model accurately predicted the pull-in voltage shift under different pulse powers and duty cycles. By comparing the power capacity of switches made of aluminum or molybdenum, a new figure of merit is proposed for selecting the optimum material for the fabrication of high-power MEMS capacitive switches.
    Microwave Conference, 2009. EuMC 2009. European; 11/2009