Brandon Harrington

Bio: Brandon Harrington is an academic researcher from Oklahoma State University–Tulsa. The author has contributed to research in topics: Resonator & Q factor. The author has an hindex of 11, co-authored 19 publications receiving 502 citations. Previous affiliations of Brandon Harrington include Oklahoma State University–Stillwater.

In-plane acoustic reflectors for reducing effective anchor loss in lateral?extensional MEMS resonators

Abstract: In this paper, novel in-plane acoustic reflectors are proposed to enhance the quality factor (Q) in lateral-mode micromachined resonators. Finite element coupled-domain simulation is used to model anchor loss and to estimate the relative change in the resonator's performance without and with the inclusion of acoustic reflectors. Several 27 and 110 MHz AlN-on-silicon resonators are fabricated and measured to validate the theoretical and simulated data. An average Q enhancement of up to 560% is reported for specific designs with reflectors over the same resonators without reflectors. The measured results trend well with the simulated data and support that the acoustic reflectors can reduce the overall anchor loss with minimum modification in the resonator design.

A 76 dB $\Omega $ 1.7 GHz 0.18 $\mu$ m CMOS Tunable TIA Using Broadband Current Pre-Amplifier for High Frequency Lateral MEMS Oscillators

Abstract: This paper reports on the design and characterization of a high-gain tunable transimpedance amplifier (TIA) suitable for gigahertz oscillators that use high-Q lateral micromechanical resonators with large motional resistance and large shunt parasitic capacitance. The TIA consists of a low-power broadband current pre-amplifler combined with a current-to-voltage conversion stage to boost the input current before delivering it to feedback voltage amplifiers. Using this approach, the TIA achieves a constant gain of 76 dB-Ohm up to 1.7 GHz when connected to a 2 pF load at the input and output with an input-referred noise below 10 pA/√(Hz) in the 100 MHz to 1 GHz range. The TIA is fabricated in a 1P6M 0.18 μm CMOS process and consumes 7.2 mW. To demonstrate its performance in high frequency lateral micromechanical oscillator applications, the TIA is wirebonded to a 724 MHz high-motional resistance (Qunloaded ≈ 2000, Rm ≈ 750 Ω, CP ≈ 2 pF) and a 1.006 GHz high-parasitic (Qunloaded ≈ 7100, Rm ≈ 150 Ω, CP ≈ 3.2 pF) AIN-on-Silicon resonator. The 724 MHz and 1.006 GHz oscillators achieve phase-noise better than -87 dBc/Hz and -94 dBc/Hz @ 1 kHz offset, respectively, with a floor around -154 dBc/Hz. The 1.006 GHz oscillator achieves the highest reported figure of merit (FoM) among lateral piezoelectric micromechanical oscillators and meets the phase-noise requirements for most 2G and 3G cellular standards including GSM 900 MHz, GSM 1800 MHz, and HSDPA.

Turnover Temperature Point in Extensional-Mode Highly Doped Silicon Microresonators

Abstract: This paper demonstrates the existence of a local zero temperature coefficient of frequency (i.e., turnover point) in extensional-mode silicon microresonators, fabricated on highly n-type-doped substrates and aligned to the [100] crystalline orientation. It is shown through both theoretical analysis and finite-element simulation that the turnover point in thin-film piezoelectric-on-silicon (TPoS) resonators is a function of doping concentration and orientation. Moreover, the turnover point can be adjusted by changing the thickness ratio of Si and the piezoelectric film (e.g., AlN) in the resonant structure. In order to experimentally validate this result, similar resonators are fabricated on silicon-on-insulator substrates, and the temperature variation of frequency is measured. An overall temperature-induced frequency variation of less than 245 ppm is measured over the range of -40 °C-85 °C for an ~ 25-MHz TPoS resonator aligned to the [100] plane. This is more than a 15-times reduction with respect to the uncompensated conventional silicon resonators reported before. This work is a significant step toward strengthening silicon's position as an alternative resonator technology in the quartz-dominated stable oscillator market.

Toward ultimate performance in GHZ MEMS resonators: Low impedance and high Q

Abstract: In this paper we report a ∼1GHz lateral extensional thin-film piezoelectric-on-substrate (TPoS) resonator with an unloaded quality factor (Q) of 6700 in air (frequency-quality factor product of 6.6×1012), a motional impedance of ∼160Ω, and a linear thermal coefficient of frequency of −29ppm. To achieve such low impedance the 21st harmonic resonance mode of a single crystalline silicon block is excited while the near-resonance spurs are suppressed by rigidly supporting the resonator with multiple anchors. Results measured from identical devices each supported with various anchor designs are compared and the effectiveness of increasing rigidity to remove the near-resonance distortions is confirmed. With the reported performance in this work, the fabricated ∼1 GHz resonator is suitable for very low-power and low-noise high-frequency oscillator applications.

Electronic Temperature Compensation of Lateral Bulk Acoustic Resonator Reference Oscillators Using Enhanced Series Tuning Technique

Abstract: This paper reports on the demonstration of series tuning for lateral micromechanical oscillators and its application for electronic temperature compensation of piezoelectric lateral bulk acoustic resonator (LBAR) micromechanical oscillators. Two aluminum nitride-on-silicon (AlN-on-Si) piezoelectric LBARs, one operating at 427 MHz (Rm ≈180 Ω, Qunloaded ≈ 1400) and the other operating at 541 MHz (Rm ≈ 55 Ω, Qunloaded ≈ 3000) are interfaced with a 13 mW three-stage tunable TIA implemented in 0.18 μm 1P6M CMOS process to sustain the oscillation. Recognizing the impact on the frequency tuning range due to the body capacitances appearing in parallel with the ports of the resonator, the TIA uses parasitic cancellation techniques to neutralize this effect and boost the tuning range of 427 MHz and 541 MHz oscillators, by as much as 12× to 810 ppm and 1,530 ppm, respectively, with negligible impact on the phase noise performance. The shunt parasitic capacitor is either resonated out with an active inductor or is cancelled out by using a single-terminal negative capacitor of equal value. However, the oscillator that uses negative capacitance parasitic cancellation yields larger tuning. This extended tuning range is used for temperature compensation. A 2 mW bandgap-based temperature compensation circuit which uses second-order parabolic approximation is fabricated on the same chip. Using this temperature compensation circuit has lowered the overall frequency drift of a 427 MHz tunable oscillator using negative capacitance cancellation from ±390 ppm to ±35 ppm in the -10°C to 70°C temperature range. The phase noise of this oscillator reaches -82 dBc/Hz at 1 kHz offset. The total phase noise variation for offset frequencies below 10 kHz is under 5 dB within the specified tuning range, and the best phase noise floor is under -147 dBc/Hz . Due to the higher Q and lower insertion loss of the resonating tank, the 541 MHz oscillator achieves -86 dBc/Hz at 1 kHz offset, and lower phase noise floor of -158 dBc/Hz.

Piezoelectric aluminum nitride thin films for microelectromechanical systems

Abstract: This article reports on the state-of-the-art of the development of aluminum nitride (AlN) thin-film microelectromechanical systems (MEMS) with particular emphasis on acoustic devices for radio frequency (RF) signal processing. Examples of resonant devices are reviewed to highlight the capabilities of AlN as an integrated circuit compatible material for the implementation of RF filters and oscillators. The commercial success of thin-film bulk acoustic resonators is presented to show how AlN has de facto become an industrial standard for the synthesis of high performance duplexers. The article also reports on the development of a new class of AlN acoustic resonators that are directly integrated with circuits and enable a new generation of reconfigurable narrowband filters and oscillators. Research efforts related to the deposition of doped AlN films and the scaling of sputtered AlN films into the nano realm are also provided as examples of possible future material developments that could expand the range of applicability of AlN MEMS.

A review on coupled MEMS resonators for sensing applications utilizing mode localization

Abstract: In this paper, we review a recent technology development based on coupled MEMS resonators that has the potential of fundamentally transforming MEMS resonant sensors. Conventionally MEMS resonant sensors use only a single resonator as the sensing element, and the output of the sensor is typically a frequency shift caused by the external stimulus altering the mechanical properties, i.e. the mass or stiffness, of the resonator. Recently, transduction techniques utilizing additional coupled resonators have emerged. The mode-localized resonant sensor is one example of such a technique. If the mode localization effect is utilized, the vibrational amplitude pattern of the resonators changes as a function of the quantity to be measured. Compared to using frequency shift as an output signal, the sensitivity can be improved by several orders of magnitude. Another feature of the mode-localized sensors is the common mode rejection abilities due to the differential structure. These advantages have opened doors for new sensors with unprecedented sensitivity.

Micromachined Resonators: A Review

Abstract: This paper is a review of the remarkable progress that has been made during the past few decades in design, modeling, and fabrication of micromachined resonators. Although micro-resonators have come a long way since their early days of development, they are yet to fulfill the rightful vision of their pervasive use across a wide variety of applications. This is partially due to the complexities associated with the physics that limit their performance, the intricacies involved in the processes that are used in their manufacturing, and the trade-offs in using different transduction mechanisms for their implementation. This work is intended to offer a brief introduction to all such details with references to the most influential contributions in the field for those interested in a deeper understanding of the material.