Min-Wu Kim

3-terminal nanoelectromechanical switching device in insulating liquid media for low voltage operation and reliability improvement

A nanoelectromechanical (NEM) switching device is developed with a new technique involving a liquid medium. Operation voltage is reduced by about 40% and the number of switching cycles with reliable device performance is improved dramatically, more than 5-fold. The device has a 50 nm thick TiN cantilever with a 40 nm air-gap. A CMOS compatible process is employed.

An Electrostatically Actuated Stacked-Electrode MEMS Relay With a Levering and Torsional Spring for Power Applications

This paper reports on a novel electrostatically actuated microelectromechanical systems (MEMS) relay for use in power-switching applications. It features a levering and torsional spring to enhance the stand-off voltage and contact endurance by means of an active-opening scheme. The proposed relay is based on a unique stacked-electrode structure and a soft insulating layer under the contact material that make it possible to obtain extremely low contact resistance, resulting in high current driving capability and reliable contact endurance. The fabricated relay demonstrated actuation voltages under 40 V, a switching time of 230 μs, and a maximum stand-off voltage of 360 V, which is the highest level among electrostatically actuated MEMS relays reported to date. The contact resistance was under 5 mΩ at 40 V of applied voltage, and more than 1 A could be carried. The contact reliability in a hot-switching condition was investigated for various dc current levels. At a current of 10 mA, the relay operated for more than 107 cycles before the test was stopped. In addition, the permanent contact stiction during switching operation at a 200-mA current level was overcome with a pull-off (active-opening) voltage of 90 V by the levering and torsional spring. Using this healing process, a device that failed at about 104 switching cycles in the 200-mA hot-switching mode was revived and reoperated with negligible contact resistance variation, lasting up to 4.9 ×105 cycles, constituting an order-of-magnitude enhancement in the lifetime even after failure.

Nanowire mechanical switch with a built-in diode.

Figure 1. Schematic diagramof a cross-point switch (a), which consists of a Cartesian matrix of orthogonal wires with an air gap at each intersection. The switch at each intersection can be turned on and off by The main driving engine of the IT revolution has been geometry miniaturization of transistors. This has been accomplished with a striking development in microfabrication technology, referred to as ‘‘Moore’s law;’’: the number of transistors on an integrated circuit (IC) doubles every 2 years, and industrial guidelines enable multiple devices to be integrated within a given chip area. However, as the gate insulator thickness shrinks below 2 nm and the distance between the source and drain is reduced below 50 nm, gate leakage and subthreshold leakage current flow even though the transistor is supposed to be off. Standby power when devices are supposed to be in the off state therefore occupies a significant portion of total power consumption. In addition, this situation has pushed the metal–oxide–semiconductor (MOS) transistor to the end-point of the international technology roadmap for semiconductors (ITRS). Thus, the development of a new device that consumes low power is an important undertaking. In the mechanical switch, since two electrodes are physically separated in the off state, the power consumption in the off state is ideally zero. In particular, as the accumulated heritage from semiconductor fabrication technology enables device sizes from the microto nanoscale regime, realization of a mechanical switch on the nanoscale will become more feasible. In the previously proposed approach, two terminal mechanical switches are arranged in a cross-point structure (Figure 1a). A bistable property of the cross-point structure also leads to a basis of binary digits, where information is detected by measuring the contact resistance at the cross-point: high contact resistance at the switch-off state (Figure 1b) or low contact resistance at the switch-on state (Figure 1c). These cross-point devices have been explored by the bottom-up assembly of various materials, such as carbon nanotubes, silicon–

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.

Complementary Dual-Contact Switch Using Soft and Hard Contact Materials for Achieving Low Contact Resistance and High Reliability Simultaneously

This paper reports a dual-contact microelectromechanical switch, which consists of two contacts in a single switch: one with a soft contact material and the other with a hard contact material to achieve low contact resistance and high reliability at the same time under hot switching conditions. In a single switching operation, the proposed dual-contact switch makes contact twice in sequence, where the first contact is made with a hard contact material (Pt-to-Pt) that can withstand an abrupt hot switching condition (high electric field or micro-arcing). The second contact is then accomplished with the soft contact material (Au-to-Au) that has low-contact resistance, through which most of the current flows. In contrast, when the switch releases contact, the Au-to-Au contact is initially detached, and this is followed by the release of the Pt-to-Pt contact. In this way, the dual-contact switch showed longer lifetime than that of a single Au-to-Au contact-only switch by up to fortyfold, and even better lifetime than that of a single Pt-to-Pt contact-only switch by more than two times in open laboratory environments (unpackaged). At the same time, contact resistance of the dual-contact switch was under 0.3 Ω at 50 V of the gate voltage, which is more than seven times smaller than that of the single Pt-to-Pt contact-only switch (2.2 Ω), due to the Au-to-Au contact sub-switch (the contact resistance of the single Au-to-Au contact-only switch was 2.2 Ω).

Modeling, fabrication and demonstration of a rib-type cantilever switch with an extended gate electrode

This paper presents the modeling, fabrication and measurement results of a rib-type cantilever switch with an extended gate electrode. In contrast to a conventional cantilever, it has a pull-in voltage that can be easily reduced and its dynamic bounce can be suppressed because the gate electrode is extended fully to the end of the beam. To investigate the static characteristics of the rib-type cantilever switch, the pull-in voltage is analytically compared to that of a conventional switch. We then numerically solve the dynamic Euler beam equation by introducing a new quasi-static contact model to predict the dynamic characteristics. Based on the modeling results, we successfully designed, fabricated and evaluated the rib-type cantilever switch. When the proposed cantilever switch was used with a newly optimized design of the bottom electrode, the pull-in voltage was reduced from 46.3 to 27.5 V (41% reduction). The dynamic response was measured both in air and low vacuum. The switching time was about 60% less than that of a conventional cantilever owing to the suppressed dynamic bounce. In addition, our measurements confirm that the proposed rib-type cantilever switch can endure over three times its pull-in voltage.

Monolithic integration of NEMS-CMOS with a Fin Flip-flop Actuated Channel Transistor (FinFACT)

Monolithic integration of NEMS-CMOS for a mechanically flip-flopped fin memory transistor is demonstrated via full CMOS process technology. An independent-gate (IG) FinFET is employed for CMOS logic, and a fin flip-flop actuated channel is used for NEMS memory. As the fin is actuated between the flip-flopped states, the proposed NEMS memory is referred to as a Fin Flip-flop Actuated Channel Transistor (FinFACT). The bistable mechanical flexure of the fin determines the binary memory state, which is sensed by the current flow of the transistor. The FinFACT demonstrates an excellent sensing current window (I<inf>on</inf>/I<inf>off</inf>≫10⁷), a long data retention time (τ≫10³ sec), and good endurance characteristics (cycle≫10³) in air.

A Complementary Dual-Contact MEMS Switch Using a “Zipping” Technique

This paper presents a microelectromechanical systems contact switch having both hard and soft contact materials in a single cantilever-type switching device. It operates with a zipping mechanism within which both contact materials (Pt-to-Pt and Au-to-Au) make individual contact sequentially and then detach in a reverse sequence to take advantage of both contact materials: low contact resistance and high reliability in a hot switching condition. In addition, an extended gate electrode and double T-shape cantilever beam structures effectively facilitate the sequential actuation. The fabricated switch successfully demonstrated a “dual-contact concept”-it made two sequential contacts at 31 (Pt-to-Pt) and 56 V (Au-to-Au) and it was then detached at 49 (Au-to-Au) and 23 V (Pt-to-Pt) in a single switching operation. Also, it achieved a low contact resistance of 0.3-0.5 Ω (including beam and some portion of the signal line resistances) at gate voltage from 60 to 70 V owing to the Au-to-Au contact in the device. Simultaneously, negligible contact resistance variation was observed during 2 × 106 cycles at a voltage/current level of 10 V/10 mA under hot switching and unpackaged environments, representing >100-fold longer lifetime than that of a conventional Au-to-Au cantilever switch fabricated on the same wafer.

High-Performance Hybrid Complementary Logic Inverter through Monolithic Integration of a MEMS Switch and an Oxide TFT

A hybrid complementary logic inverter consisting of a microelectromechanical system switch as a promising alternative for the p-type oxide thin film transistor (TFT) and an n-type oxide TFT is presented for ultralow power integrated circuits. These heterogeneous microdevices are monolithically integrated. The resulting logic device shows a distinctive voltage transfer characteristic curve, very low static leakage, zero-short circuit current, and exceedingly high voltage gain.

A mechanical and electrical transistor structure (METS) with a sub-2 nm nanogap for effective voltage scaling

A mechanical and electrical transistor structure (METS) is proposed for effective voltage scaling. The sub-2 nm nanogap by atomic layer deposition (ALD) without stiction and the application of a dielectric with high-permittivity allowed the pull-in voltage of sub-2 V, showing the strength of the mechanical actuation that is hard to realize in a typical complementary metal-oxide-semiconductor (CMOS) transistor. The results are verified by simulation and interpreted by the numerical equation. Therefore the METS can pave a new way to make a breakthrough to overcome the limits of CMOS technology.