Hyun-Ho Yang

Metal-oxide-semiconductor field effect transistor humidity sensor using surface conductance

This letter presents a metal-oxide-semiconductor field effect transistor based humidity sensor which does not use any specific materials to sense the relative humidity. We simply make use of the low pressure chemical vapor deposited (LPCVD) silicon dioxide’s surface conductance change. When the gate is biased and then floated, the electrical charge in the gate is dissipated through the LPCVD silicon dioxide’s surface to the surrounding ground with a time constant depending on the surface conductance which, in turn, varies with humidity. With this method, extremely high sensitivity was achieved—the charge dissipation speed increased thousand times as the relative humidity increased.

An Extremely Low Contact-Resistance MEMS Relay Using Meshed Drain Structure and Soft Insulating Layer

This paper presents an electrostatically actuated microelectromechanical systems (MEMS) relay with a stacked-electrode structure having meshed drain electrode and a soft dielectric layer under the contact material to achieve high contact force and low hardness simultaneously, with the aim of providing ultralow contact resistance. In particular, a novel method for laying benzocyclobutene polymer under the contact layer to enlarge the contact area by reducing the effective hardness is proposed and theoretically analyzed. This could reduce the contact resistance by more than half in the case of an Au-Au contact. The fabricated devices have pull-in voltage of 32-43 V, switching time of 25 μs, and current driving capability of 350 mA in a hot-switching condition. Furthermore, the achieved minimum contact resistance is as low as 4 mΩ, which, to our knowledge, is the lowest value reported to date. In addition, negligible variation of contact resistance was observed during 1.4 × 106 hot-switching cycles in a 100-mA current level. The fabricated MEMS relay in the relatively low current of 1 mA was able to operate for more than 100 million cycles without failure before the test was stopped.

Mechanically Operated Random Access Memory (MORAM) Based on an Electrostatic Microswitch for Nonvolatile Memory Applications

We proposed and demonstrated a mechanically operated random access memory (MORAM) based on an electrostatically actuated metallic microswitch for nonvolatile memory applications. The metallic microswitch-based MORAM successfully showed program and erase operations, wherein the microswitch had an essentially zero off current, an abrupt switching with less than 1 mV/dec, and an on/off current ratio over 107, and its stored charge was investigated with the metal-oxide-semiconductor (MOS) capacitor. Moreover, first reported were an endurance of up to 105 cycles in air ambient and a retention time of more than 104 s in vacuum ambient.

An ultra-low voltage MEMS switch using stiction-recovery actuation

In this paper, an ultra-low voltage microelectromechanical system (MEMS) switch is proposed, modeled and demonstrated. Through the introduction of torsional hinges, stiction-recovery actuation was possible, and thus irreversible stiction could be overcome. Owing to this see-saw-like actuation, the switch could be freely designed to have low stiffness resulting in an ultra-low actuation voltage. The proposed switch shows an actuation voltage of around 3 V, which is especially low compared with typical values of several tens of volts in conventional microelectromechanical switches. Variation of the actuation voltage stayed under 12% during 106 cycles. Switching performance was degraded by an increase of contact resistance rather than in-use stiction. Using the proposed switches, low-voltage mechanical logic gates were also proposed and successfully demonstrated, operating at VDD of 3 V.

Maneuvering Pull-in Voltage of an Electrostatic Micro-switch by Introducing a Pre-charged Electrode

A new method to greatly reduce and control the pull-in voltage of an electrostatic micro-switch was developed, simply by introducing a pre-charged floating electrode. For showing feasibility, the conventional electrostatic micro-switch is used with substrate biasing. Using this method, the original pull-in voltage of 48 V was reduced to 3 V and symmetrical hysteric curve around 0 V was obtained like an ideal non-volatile memory.

Double Bow-Tie Slot Antennas for Wideband Millimeter-Wave and Terahertz Applications

This paper presents millimeter-wave and terahertz double bow-tie slot antennas on a synthesized elliptical silicon lens. Two different antennas are designed to cover 0.1-0.3 and 0.2-0.6 THz, respectively. The double bow-tie slot antenna results in a wide impedance bandwidth and 78-97% Gaussian coupling efficiency over a 3:1 frequency range. A wideband coplanar-waveguide low-pass filter is designed using slow-wave techniques, and the measured filter response shows an S21 <; -25 dB over a 3:1 frequency range. Absolute gain measurements done at 100-300 GHz and 200-600 GHz confirm the wideband operation of this design. The double bow-tie slot antenna is intended to fill the gap between standard double-slot antennas and log periodic and sinuous antennas, with applications areas in radio astronomy and imaging systems.

An insulating liquid environment for reducing adhesion in a microelectromechanical system

Stiction has been one of the major failure problems in microelectromechanical systems (MEMS). As a solution for stiction failure, we investigated an insulating liquid environment for MEMS to eliminate adhesion force. We speculated that three forces—capillary, solid-solid contact, and van der Waals (vdW) forces decrease when the devices are operated in an insulating liquid environment. In the experiment, the adhesion force of the devices was measured to be 42.8 μN on average in air, whereas it decreased to 2.52 μN on average in the insulating liquid, corresponding to a remarkable 94.1% decrement.

A simple breathing rate-sensing method exploiting a temporarily condensed water layer formed on an oxidized surface

We describe a very simple breathing rate-sensing method that detects a significant electric current change between two metal electrodes on an oxidized surface. The current change is caused by the formation of a water layer from exhaled breath. We discovered that breathing onto the oxidized surface causes instant water condensation, and it generates 20 times increased current than that measured in the inhalation period. The condensed water quickly evaporates, enabling us to detect dynamic human breathing in real time. We also investigated the breathing rate sensor by varying the relative humidity, temperature, and breathing frequency and confirmed its potential for practical applications.

An electrostatic micromechanical biosensor for electrical detection of label-free DNA

An electrostatic micromechanical biosensor is demonstrated for the label-free electrical detection of DNA, based on electrostatic actuation of a double-clamped micromechanical cantilever by driving gate electrodes to establish a current path through drain and source electrodes. Intrinsic charges in DNA alter surface charges on the gate by pre-charging concept and change the pull-in voltage (VPI), the voltage required to bring the suspended cantilever into contact with the drain electrode by induced electrostatic force. Its operation principle is verified by a numerical simulation and a capacitive model. The proposed biosensor represents a breakthrough for practical exploitation of electro-mechanical based sensors.

A new method of driving an AMOLED with MEMS switches

We newly propose an active-matrix organic light-emitting diode (AMOLED) pixel circuit composed of MEMS switches and its digital driving method for grayscale modulation using time ratio gray scale (TRGS) scheme. Developing a spice compatible model of the MEMS switch, the proposed driving method has been successfully verified by circuit simulation. Current driving capability of the fabricated MEMS switch is evaluated with wiring them to the OLED pixel which is separately fabricated. We could obtain the ON current of 11.4 muA from the wired OLED and MEMS switch with a VDD of 10 V. The fabricated MEMS switch with length of 50 mum and width of 10 mum showed the pull-in voltage of 58 V and total on-state resistance (with leads) of 20 Omega. We successfully demonstrated the grayscale changes of an OLED by modulating the duty ratio of the control signal at 60 Hz.