Dana Weinstein

The Resonant Body Transistor

This paper introduces the resonant body transistor (RBT), a silicon-based dielectrically transduced nanoelectromechanical (NEM) resonator embedding a sense transistor directly into the resonator body. Combining the benefits of FET sensing with the frequency scaling capabilities and high quality factors (Q) of internal dielectrically transduced bar resonators, the resonant body transistor achieves >10 GHz frequencies and can be integrated into a standard CMOS process for on-chip clock generation, high-Q microwave circuits, fundamental quantum-state preparation and observation, and high-sensitivity measurements. An 11.7 GHz bulk-mode RBT is demonstrated with a quality factor Q of 1830, marking the highest frequency acoustic resonance measured to date on a silicon wafer.

Dielectrically Transduced Single-Ended to Differential MEMS Filter

A single-ended input to balanced output 425MHz mechanically coupled electromechanical filter is presented. This technology provides 1MHz channel select filtering while eliminating the need for RF switches and baluns in front-end transceivers. The filter achieves 8dB insertion loss with -50dB stop-band rejection and -48dB common-mode suppression

Internal Dielectric Transduction of a 4.5 GHz Silicon Bar Resonator

This paper presents experimental verification of frequency scaling in an internal dielectric transduced resonator. A silicon bar resonator is excited in its 3rd and 9th longitudinal harmonic modes at 1.53 and 4.51 GHz, respectively. The resonator demonstrates a 2 dB improvement in transduction efficiency in its 9th harmonic relative to its 3rd harmonic, normalized to the quality Q of the resonance. This result is in close agreement with theory, promising low- impedance transduction of silicon bulk acoustic resonators at frequencies exceeding 10 GHz.

Internal Dielectric Transduction in Bulk-Mode Resonators

This paper investigates electrostatic transduction of a longitudinal-mode silicon acoustic resonator with internal dielectric films. Geometric optimization of internal dielectrically transduced resonators is derived analytically and shown experimentally. Analysis of internal dielectric transduction shows a maximum transduction efficiency with thin dielectric films at points of maximum strain of the desired resonant mode. With this design optimization, a silicon bar resonator is realized with a ninth harmonic resonance of 4.5 GHz and a quality factor of over 11 000, resulting in a record high f middotQ product in silicon of 5.1 times 1013. The novel dielectric transducer demonstrates improved resonator performance with increasing frequency, with optimal transduction efficiency when the acoustic wavelength is twice the dielectric thickness. Such frequency scaling behavior enables the realization of resonators up to the super-high-frequency domain.

Mechanical Coupling of 2D Resonator Arrays for MEMS Filter Applications

This paper presents a study of mechanical coupling in 2D resonator arrays for filter applications. A robust coupling design for 2D array filters, comprised of weak coupling in one dimension and strong coupling in the second, is demonstrated experimentally and compared with weakly coupled and electrically summed 2D resonator array filters. Effects of inherent disorder in resonator arrays due to fabrication variations are minimized in this mechanical coupling scheme, averaging over resonator mismatch to form a smooth pass-band. The strongly-coupled 2D filter improves insertion loss and ripple without degradation in filter shape factor or stop-band rejection relative to its ID counterpart.

Channel-Select Micromechanical Filters Using High-K Dielectrically Transduced MEMS Resonators

This paper demonstrates electrically and mechanically coupled channel-select filters comprised of dielectrically transduced thickness shear mode resonators. The filters are fabricated on the 3.2 μm thick device layer of a heavily doped SOI wafer with a 30 nm thick hafnium dioxide film sandwiched between the polysilicon electrodes and the silicon device layer. An 809 MHz half-wave thickness shear resonator is demonstrated with a quality factor (Q) of 7,800 in air and a motional impedance (RX) of 59 Ω. An array of such resonators is coupled electrically and mechanically to form dielectrically transduced MEMS filters. Electrically coupled channel-select filters with 814 MHz center frequency, 600 kHz bandwidth, -4 dB insertion loss (IL) and < 1dB pass-band ripple are presented. In addition, a mechanically coupled 804 MHz center frequency filter is demonstrated exhibiting -34 dB stop-band rejection and a 20 dB shape factor of 1.28.

Size-dependent modulation of carrier mobility in top-down fabricated silicon nanowires

We have investigated the size dependence of field-effect mobility in top-down fabricated Si nanowires (NWs). We find that electron mobility increases while hole mobility decreases with the NW width. The observed trends are opposite of what we expect based on facet-dominated transport. We simulate charge densities and investigate the effect of gate stack-induced stress in an effort to explain these trends. We find that the use of piezoresistive coefficients for bulk or thin-film Si does not give sufficient change in mobility to reverse the facet-driven mobility trend. We suggest further investigation into the contribution of one-dimensional NW corner effects.

Resonant Body Transistors in IBM's 32 nm SOI CMOS Technology

This paper presents unreleased CMOS-integrated MEMS resonators fabricated at the transistor level of IBMs 32SOI technology and realized without the need for any postprocessing or packaging. In this technology, resonant body transistors (RBTs) are driven capacitively and sensed piezoresistively using an n-channel field effect transistor (FET). Acoustic Bragg Reflectors (ABRs) are used to localize acoustic vibrations in the unreleased resonators completely buried under the CMOS metal stack and surrounded by low-κ dielectric. FET sensing is analytically compared with alternative active and passive sensing mechanisms to benchmark CMOS-MEMS resonator performance with frequency scaling. Experimental results from the first generation hybrid CMOS-MEMS RBTs show RBTs operating above 11 GHz with Qs of 24-30 and footprints of 5 × 3 μm. Comparative behavior of devices with design variations is used to demonstrate the effect of ABRs on spurious mode suppression. In addition, the performance of the RBTs is compared with passive electrostatic resonators, which show no discernible peak. Finally, temperature stability of <;3 ppm/K due to complimentary materials in the CMOS stack is analytically and experimentally verified.

L-band Lamb mode resonators in Gallium Nitride MMIC technology

We present a theoretical and experimental study of L-band (1-2 GHz) Lamb mode resonators in Gallium Nitride (GaN) monolithic microwave IC technology. These resonators leverage Au-free metallization and optimized anchors, enabling f·Q products up to 5.5×1012, the highest reported in GaN resonators to date. These devices also demonstrate the highest electromechanical coupling (keff2 of 0.39%) measured in GaN resonators using an interdigitated transducer in the absence of a bottom electrode. Achieving such high values of f·Q and keff2, these GaN MEMS resonators can enable channel select filters for wireless communications, with wide bandwidth tuning capabilities (0.18-0.8 MHz) at 1-2 GHz range.

Acoustic Bragg reflectors for Q-enhancement of unreleased MEMS resonators

This work presents the design of acoustic Bragg reflectors (ABRs) for unreleased MEMS resonators through analysis and simulation. Two of the greatest challenges to the successful implementation of MEMS are those of packaging and integration with integrated circuits. Development of unreleased RF MEMS resonators at the transistor level of the CMOS stack will enable direct integration into front-end-of-line (FEOL) processing, making these devices an attractive choice for on-chip signal generation and signal processing. The use of ABRs in unreleased resonators reduces spurious modes while maintaining high quality factors. Analysis on unreleased resonators using ABRs covers design principles, effects of fabrication variation, and comparison to released devices. Additionally, ABR-based unreleased resonators are compared with unreleased resonators enhanced using phononic crystals, showing order of magnitude higher quality factor (Q) for the ABR-based devices.