Yong-Hoon Yoon

A Highly Reliable MEMS Relay With Two-Step Spring System and Heat Sink Insulator for High-Power Switching Applications

This paper reports a highly reliable electrostatic microelectromechanical systems (MEMS) relay for high-power switching applications. The main proposal to elevate reliability is to reduce thermal damage in the contact area. Since a contact resistance is the key parameter determining the amount of Joule-heating and the corresponding thermal damage, we devised a unique spring structure to maximize the contact force (resulting in a low contact resistance) using a reasonable actuation voltage named a two-step spring system. Another important feature was applied to alleviate Joule-heating, which is to use an insulator having high thermal conductivity to dissipate the generated heat efficiently, named a heat sink insulator. The fabricated MEMS relay exhibited 2 mΩ in contact resistance, which is the lowest level reported so far with an actuation voltage of 45 V. Reliability was remarkably enhanced over ten times by the heat sink insulator. Consequently, by applying these two approaches simultaneously, the fabricated MEMS relay was successfully operated up to the 5.3 ×106 cycles at 1 V/200 mA in ambient air and hot switching condition, which is the highest reliability reported at that power level.

Voltage-Controlled

In a conventional parallel plate MEMS variable capacitor, the capacitance versus voltage response (C-V response) has been deterministic. In this work, the C-V response is tuned versatilely through the application of a control voltage to an additional electrode in order that the initial gap between the parallel capacitor plates is set by the control voltage. Then, the capacitor plates are lifted (capacitance decreases) as the actuation voltage applied to the levering actuator increases. In this manner, the shape of the C-V response can be controlled even after the device is fabricated. At a zero control voltage, the fabricated MEMS variable capacitor exhibited a convex shape in the C-V response (i.e., the capacitance decreases slowly in the low actuation voltage region and rapidly in the high actuation voltage region). When 3 V was applied to the control voltage, the capacitor exhibited an almost linear C-V response with a linearity factor of 0.999. At 5 V of control voltage, the C-V response changed to a relatively concave shape (i.e., the capacitance decreases rapidly in the low actuation voltage region and slowly in the high actuation voltage region). The capacitance tuning ratio of the fabricated device exceeded 120% at all control voltages. The proposed C-V response tuning capability is vital and amenable to various circuit demands.

C{-}V

Since a microelectromechanical (MEM) switch with an electrostatically actuated cantilever was first demonstrated by Petersen in 1978 [1], MEM switches have actively been researched by many research groups. However, comparing with the conventional metal-oxide-semiconductor field-effect transistor (MOSFET), MEM switches are still suffering from their high actuation voltage and insufficient operational reliability, which still remain as a difficult challenge to many MEMS researchers and hinder commercialization of the MEM switches. In this work, we look at what lies behind these difficulties in MEM switches and illustrate bright ideas that have been sought to enhance the actuation voltage and switch endurance (lifetime) problems.

Response Tuning in a Parallel Plate MEMS Variable Capacitor

This paper reports an innovative and simple three-dimensional (3-D) reshaping (plastic deformation) technique in MEMS devices by solely electrical control with ultrafine tuning resolution. The proposed plastic deformation technique adopted the creep phenomenon to achieve the desired plastic deformation. While voltage input induced stress on the device to start the creep phenomenon, Joule heating was applied to accelerate the creep phenomenon. Then, plastic deformation was successfully demonstrated with solely electrical control, where the tuning resolution was demonstrated at a sub-100nm level.

Efforts toward ideal microelectromechanical switches

This paper reports a unique 4-terminal MEMS relay (actuation is electrically isolated with signal passage) employing a novel one-contact design to overcome high contact resistance problem of the conventional 4-terminal MEMS relay which utilizes a typical two-contact design. The fabricated 4-terminal MEMS relay with the one-contact design demonstrated a contact resistance of 18 mΩ, which is two order-of-magnitude lower value than that of the conventional two-contact design. To the best of our knowledge, this result is the lowest value in the 4-terminal MEMS relay and comparable value with the state-of-the-art in 3-terminal MEMS relay [14]. In addition, the relay was operated up to 1.1 × 106 cycles at 1 V / 50 mA in an air and hot switching condition with negligible contact resistance variation. The lifetime is 10 times longer than that of the conventional 4-terminal MEMS relay.

Three-dimensional (3-D) reshaping technique in MEMS devices by solely electrical control with ultrafine tuning resolution

This paper reports a simple microelectromechanical systems (MEMS) packaging method as one way of adhesive bonding at room temperature and atmospheric pressure. The adhesive material spreads into the patterned bonding interface perfectly only by capillary force and cured by ultraviolet (UV) exposure only. As a result of the moisture permeation test in the accelerated condition (85 °C / 85 % relative humidity(RH)), the proposed packaging method is expected to prevent moisture permeating over 14.4 years in the normal condition (25 °C / 50 % RH). Also, a fabricated MEMS LC-resonator showed only about 5 % difference of the resonant frequency after packaging, which demonstrates the packaging process does not degrade the MEMS device. Thus, the proposed packaging method can be easily used especially in the case of temperature sensitive device packaging.