Adam Fruehling

A single-crystal silicon DC-40 GHz RF MEMS switch

This paper presents a new DC-40 GHz RF MEMS switch whose moving part is made of single-crystal silicon (SCS). Unlike thin-film metals commonly employed in RF MEMS switches, SCS is essentially defect-free, has well known and repeatable material properties and is virtually stress free. This makes the switch design insensitive to process variations and amenable to high-yield manufacturing. Measured RF switches exhibit an on state insertion loss of less than 0.3 dB and an off state isolation of higher than 30 dB up to 40 GHz. Measured switching time is less than 4 us.

Cyclic evolution of bouncing for contacts in commercial RF MEMS switches

This paper systematically investigates for the first time the evolution of switch bounce for the Omron 2SMES-01 switch as a function of lifetime cycling. We demonstrate that the first bounce duration monotonically increases by as much as 20% over 200 million cycles. In addition, the amplitude of tertiary bounces monotonically increase by as much as 100 % over the same interval with the spontaneous occurrence of new bounces persisting as cycle count increases. Measurement of switch bouncing provides a readily accessible form of transient analysis of RF MEMS contacts and has the potential to become an indispensable tool for in-situ switch diagnostics related to adhesion forces, contact hardening, and film formation. A novel automated platform for studying both static and dynamic switch characteristics over the lifetime of an RF MEMS switch is demonstrated as well.

Real-time monitoring of contact behavior of RF MEMS switches with a very low power CMOS capacitive sensor interface

This paper presents the first ultra-low power, fully electronic methodology for real-time monitoring of the dynamic behavior of RF MEMS switches. The measurement is based on a capacitive readout circuit composed of 67 transistors with a 105 μm × 105 μm footprint consuming as little as 60 μW. This is achieved by accurately sensing the capacitance change around the contact region at sampling rates from 10 kHz to 5 MHz. Experimental and simulation results show that timing of not only the first contact event but also all subsequent contact bounces can be accurately measured with this technique without interfering with the switch performance. This demonstrates the potential of extending this technique to real-time on-chip dynamic monitoring of packaged RF MEMS switches through their entire lifetime and after their integration in the final system.

Nano-switch for study of gold contact behavior

In this paper we present the fabrication and characterization of a new NEMS DC switch as a vehicle to characterize Au-to-Au contacts at nano-scale. The switch consists of a 1050-nm long, 200-nm wide and 50-nm thick cantilever gold beam. The measured on-state resistance values range from 83 Ω to 640 Ω and the actuation voltages from 4 V to 22 V. All measurements are conducted at a current of 1 µA and the obtained values are in good qualitative agreement with traditional elastic-plastic contact models. The calculated switching time is 55 ns. Characterization of contacts at nano-scale will be critical for the success of NEMS devices used in ultra low-power sensors. To this end, we examine the impact of such a switch as a leakage control mechanism.

Arrays of silicon cantilevers for detecting high-G rapidly varying acceleration profiles

This work presents the first experimental study on the effectiveness of single-crystal silicon (SCS) cantilever arrays as contact-based high-G sensors in digital MEMS accelerometers. Unlike conventional designs, a digital scheme is employed where detection of a specific acceleration level is associated with a group of silicon cantilevers, which deflect and make solid-to-solid silicon contacts with the substrate. This scheme is especially useful in applications where a high-G rapidly changing acceleration profile needs to be detected with a high confidence level. The proposed designs have been successfully demonstrated up to 45,000 g, which is commonly found in impact and pyroshock phenomena, such as in multistage rocket launches and earth penetrating weapons. The arrays of beams offer high redundancy in the measured data, which is critical when used in events with severe consequences. The fabricated devices were tested using a modified Kolksy bar setup and found to have contact resistances in the order of ∼3.2±3 kΩ. Depending on the applied acceleration profile, contact bouncing is observed during testing.

RF MEMS switches for leakage control in wireless handheld devices

A new methods for controlling leakage power in handheld device was proposed. This paper presents the use of a MEMS switch as a replacement for the sleep transistor method to reduce leakage current allowing for significant improvement in the battery life of portable electronic systems.

MEMS-Based Power Gating for Highly Scalable Periodic and Event-Driven Processing

For periodic and event-driven applications with long standby times, controlling leakage is essential. This paper investigates using MEMS switches for power gating processors, which eliminates standby leakage power and allows for highly scalable processing. We show that when power gating with a MEMS switch, low technology nodes and low threshold voltages, which offer low switching energy and high speeds, are optimal. We also compare a MEMS-gated processor to two recent low leakage processors and show that it is ideal for applications with 100+ ms standby times. With CMOS compatibility on the horizon, MEMS switches are an attractive option for low-leakage applications.

Lifetime effects of drive voltage for a commercially-available ohmic-contact RF MEMS switch

This work presents the first report on the influence of actuation voltage on high-voltage-switching lifetime with a population study of commercially-available ohmic contact RF MEMS switches manufactured by Omron. For switches actuated with a bias voltage of 15% less than Omrons specified operating point a greater than 6× increase in lifetime is observed for 75% of devices. This is despite the fact that a 15% reduced voltage increases the bouncing behavior of the switch. Simulated results suggest that it is likely more important that the 15% reduced voltage decreases the impact velocity and force by 24% and 42% respectively. While the increase in switch lifetime is significant, it comes with a penalty of increased dispersion in the achieved contact resistance (1-3.1 Ω versus 1-2.5 Ω) and increased settling time (48 μs versus 13 μs).

In situ monitoring of dynamic bounce phenomena in RF MEMS switches

This paper presents the first ultra-low-power complementary metal?oxide?semiconductor (CMOS)-based measurement technique for monitoring the cold-switched dynamic behavior of ohmic radiofrequency microelectromechanical systems (RF MEMS) switches in real time. The circuit is capable of providing precise information about contact timing and ohmic contact events. Sampling of dynamic events at frequencies of 1 and 5?MHz shows contact timing accuracy of 99% when compared with real-time true-height information obtained from laser Doppler vibration data. The technique is validated for an ohmic RF MEMS switch with multiple bounces. The actuation voltage has also been designed to enhance bouncing behavior to more clearly study the performance and limits of the presented technique. More than 13?bounces are successfully captured by the electronic measurement technique. The weakest bounces exhibit vertical displacements of less than 20?nm as recorded by a laser Doppler vibrometer. This demonstrates the ability to capture precise timing information even for weak contacting events. A detailed discussion of how parasitics influence this technique is also presented for the first time.

Electrostatic fringing-field actuation for pull-in free RF-MEMS analogue tunable resonators

This paper presents the design, fabrication and measurement of the first pull-in free tunable evanescent-mode microwave resonator based on arrays of electrostatically actuated fringing-field RF-MEMS tuners. Electrostatic fringing-field actuation (EFFA) is the key on achieving a wide tunable frequency range that is not limited by the conventional pull-in instability. Furthermore, total lack of dielectric layers and no overlap between the pull-down electrode and movable beams significantly enhance the robustness of our proposed tuning mechanism by making it devoid of dielectric charging and stiction and amenable to high-yield manufacturing. The proposed electrostatic fringing-field tuners are demonstrated in a highly loaded evanescent-mode cavity-based resonator. The measured unloaded quality factor is 280?515 from 12.5 to 15.5?GHz. In addition, a 10? improvement in switching time is demonstrated for the first time for EFFA tuners in a tunable microwave component by employing dc-dynamic biasing waveforms. With dynamic biasing, the measured up-to-down and down-to-up switching times of the resonator are 190 and 148 ?s, respectively. On the other hand, conventional step biasing results in switching times of 5.2 and 8?ms for up-to-down and down-to-up states, respectively.