Yonghyun Shim

A High-Performance Continuously Tunable MEMS Bandpass Filter at 1 GHz

This paper reports a continuously tunable lumped bandpass filter implemented in a third-order coupled resonator configuration. The filter is fabricated on a Borosilicate glass substrate using a surface micromachining technology that offers hightunable passive components. Continuous electrostatic tuning is achieved using three tunable capacitor banks, each consisting of one continuously tunable capacitor and three switched capacitors with pull-in voltage of less than 40 V. The center frequency of the filter is tuned from 1 GHz down to 600 MHz while maintaining a 3-dB bandwidth of 13%-14% and insertion loss of less than 4 dB. The maximum group delay is less than 10 ns across the entire tuning range. The temperature stability of the center frequency from -50°C to 50°C is better than 2%. The measured tuning speed of the filter is better than 80 s, and the is better than 20 dBm, which are in good agreement with simulations. The filter occupies a small size of less than 1.5 cm × 1.1 cm. The implemented filter shows the highest performance amongst the fully integrated microelectromechanical systems filters operating at sub-gigahertz range.

RF switches using phase change materials

Phase change materials are attractive candidates for use in ohmic switches as they can be thermally transitioned between amorphous and crystalline states, showing several orders of magnitude change in resistivity. Phase change switches are fast, small form factor, and can be readily integrated with MEMS and CMOS electronics. As such, they have a great potential for implementing next-generation high-speed reconfigurable RF modules. In this paper, we report on the RF properties of germanium tellurium, a PC material, and its use in RF switching applications. Intrinsic resistance and capacitance at the ON (crystalline) and OFF (amorphous) states of a directly heated switch are compared and characterized. Other properties such as phase transition conditions, insertion loss, return loss, and power handling capability of the switch are also measured and analyzed.

Miniaturized UWB Filters Integrated With Tunable Notch Filters Using a Silicon-Based Integrated Passive Device Technology

This paper reports on the implementation of miniaturized ultra-wideband filters integrated with tunable notch filters using a silicon-based integrated passive device technology. An ultra-wideband bandpass filter is realized on a micromachined silicon substrate, showing an insertion loss of 1.1 dB, return loss of better than 15 dB, and attenuation of more than 30 dB at both lower and upper stop-bands, with a spurious-free response up to 40 GHz. The filter occupies only 2.9 mm 2.4 mm of die area. To address the in-band interference issues associated with ultra-wideband communication, very compact tunable notch filters are monolithically integrated with the bandpass filters. A two-pole tunable notch filter integrated with an ultra-wideband filter provides more than 20 dB rejection in the 5-6 GHz range to reject U-NII interferences, with a total footprint of 4.8 mm 2.9 mm. The power handling, linearity, and temperature stability of filters are characterized and presented in this paper.

RF MEMS Passives on High-Resistivity Silicon Substrates

Diverse RF passive devices and microelectro- mechanical systems (MEMS) can be monolithically integrated on a high-resistivity silicon (HR-Si) substrate. However, parasitic surface conduction (PSC) at the interface of HR-Si and a silicon dioxide (SiO2) passivation layer reduces the effective substrate resistivity, which in turn results in deterioration of the device quality factor (Q) and non-linearity. Trap-rich HR-Si has been proposed as a low substrate loss alternative, eliminating the problems associated with PSC. However, the full potential of trap-rich HR-Si as a common platform for implementing MEMS passives is not fully explored. In this letter, we evaluate the effectiveness of the trap-rich layer by comparing the frequency response of a number of RF passive devices fabricated on standard and trap-rich HR-Si substrates. In addition, we suggest an electromagnetic (EM) simulation setup that can be used to efficiently and accurately simulate the device performance.

A high-performance, temperature-stable, continuously tuned MEMS capacitor

This paper reports on a continuously tunable MEMS capacitor with a wide tuning range of 5∶1, high quality factor of better than 100 (at 1 GHz) at each tuned state, and self-resonance frequency of more than 13.5 GHz. The temperature stability of the capacitance in the temperature range of −50 °C to 60 °C is better than 7%, which is one of the best reported for continuously tuned capacitors. The maximum tuning speed of the capacitor is measured to be better than 40 µsec.

Non-Linearity Analysis of RF Ohmic Switches Based on Phase Change Materials

We report on a thermoelectric model that can be used to analyze the nonlinearity and power handling capability of RF switches based on phase change (PC) materials. To analyze the nonlinear behavior of the PC switches, the Poole-Frenkel effect, the variation of thermal and electrical conductance with temperature, and the effect of Joule heating with increased RF signal power are all taken into account. The simulated input third-order intercept point and the 1-dB compression point (P1dB) are compared with measured results of directly heated PC switches, showing a good agreement. Using this model, we provide insights into the effect of electrical resistance, and thermal properties, as well as the operation frequency on the switch nonlinearity and power handling capability.

Miniaturized UWB bandpass filters integrated with notch filters using a Si-based integrated passive device technology

Summary form only given, as follows. Miniaturized UWB filters with low loss, steep rejection, and spurious-free response on a silicon substrate are reported. A UWB filter is demonstrated with less than 1 dB insertion loss, more than 30 dB stop-band rejection, occupying 2.9 mm × 2.4 mm of die area. A UWB filter with a notch filter is presented having a footprint of 4.6 mm × 2.9 mm. The notch filter centered at 5.285 GHz provides a maximum attenuation of 23 dB with 10 dB bandwidth of 7% and shows excellent temperature stability.

Observation of the acoustoelectric effect in gallium nitride micromechanical bulk acoustic filters

We report on the experimental verification of the acoustoelectric effect in gallium nitride (GaN) and present a model to describe this effect in GaN thickness-mode bulk acoustic filters. Filters are fabricated using 2.2 µm thick n-type GaN on high resistivity silicon epiwafers obtained from SOITEC. Acoustoelectric effect was observed by applying an electric field parallel to c-axis, the direction of acoustic wave propagation. Improvement in the insertion loss and out-of-band rejection was observed and Q amplifications exceeding 240% was achieved. Acoustoelectric effect makes it possible to dynamically tune the frequency response of GaN resonators and filters.

A Multimetal Surface Micromachining Process for Tunable RF MEMS Passives

This paper reports on a microfabrication technology for implementing high-performance passive components suitable for advanced RF front-ends. This technology offers three metal layers with different thicknesses, one dielectric, and two sacrificial layers, enabling the fabrication of continuously tuned capacitors, capacitive and ohmic switches, as well as high- inductors all on a single chip. To demonstrate the versatility of this technology, several passive components are fabricated on a Borosilicate glass substrate . A high- tunable capacitor is fabricated exhibiting an electrostatic tuning range of more than 6 : 1. The temperature variation of capacitance from 223 to 333 K is less than 9%, and the tuning speed is better than 80 . To achieve a higher zero-bias capacitance, a tunable capacitor bank is also implemented, which can be tuned from 2.2 pF to 6.1 pF. In addition, a coupled inductor pair with self-inductances of 15 and 21 nH is implemented showing s exceeding 40 at 800 MHz. Measurements are compared with high frequency structure simulator (HFSS) electromagnetic simulations, showing good agreement. The technology reported is post-CMOS compatible and low cost.

Switchable wide tuning range bandstop filters for frequency-agile radios

This paper reports on micromachined tunable bandstop filters that exhibit an octave frequency tuning range with high stopband rejection and low out-of-band loss. In addition to continuous frequency tuning, stopband switch on-off capability is realized by employing ohmic switches along with tunable capacitors. The fully re-configurable filters in this work are fabricated using a silicon-based integrated passive device technology and are the smallest-size bandstop filters reported in the low SHF range.