Jeronimo Segovia-Fernandez

Anchor Losses in AlN Contour Mode Resonators

In this paper, we analyze possible sources of dissipation in aluminium nitride (AlN) contour mode resonators for three different resonance frequency devices (fr) (220 MHz, 370 MHz, and 1.05 GHz). For this purpose, anchors of different widths (Wa) and lengths (La) proportional to the acoustic wavelength (λ) are designed as supports for resonators in which the dimensions of the vibrating body are kept fixed. The Q extracted experimentally confirms that anchor losses are the dominant source of damping for most anchor designs when fr is equal to 220 and 370 MHz. For specific anchor dimensions (Wa/λ is in the range of 1/4-1/2) that mitigate energy leakage through the supports, a temperature-dependent dissipation mechanism dominates as seen in higher fr resonators operating close to 1.05 GHz. To describe the Q due to anchor losses, we use a finite-element method with absorbing boundary conditions. We also propose a simple analytical formulation for describing the dependence of the temperature-dependent damping mechanism on frequency. In this way, we are able to quantitatively predict Q due to anchor losses and qualitatively describe the trends observed experimentally.

Reduction of anchor losses by etched slots in aluminum nitride contour mode resonators

This paper presents a new technique to increase the quality factor, Q, of AlN Contour Mode Resonators (CMRs). The technique uses etched slots in the body of AlN CMRs to reduce energy dissipation through the anchors. The reduction of the energy lost through the supporting anchors improves the device Q without altering its electromechanical coupling, kt2. An almost 50% improvement in the Figure of Merit, FoM, defined as the product between Q and kt2, has been measured in 220 MHz AlN CMRs.

Damping in 1 GHz laterally-vibrating composite piezoelectric resonators

This paper focuses on experimentally verifying the physics of damping in 1 GHz laterally-vibrating composite piezoelectric resonators. This work confutes a previously developed theory of interfacial dissipation, a slip phenomenon occurring at the interface between dissimilar materials, which associated damping to a stress jump (or difference in Youngs moduli (ΔE)) of the materials forming the interface. This work finds that damping in 1 GHz laterally-vibrating AlN resonators could be attributed to either interfacial dissipation due to an acoustic velocity jump (Δv) or thermoelastic dissipation (TED) in the electrodes.

Thermal Nonlinearities in Contour Mode AlN Resonators

In this paper, we analyze the origin of elastic nonlinearities in aluminium nitride contour mode resonators (CMRs). Our study highlights that the nonlinear behavior is due to thermal effects when the resonators are electrically excited and the input is slowly (slow with respect to the device thermal time constant) swept through the excitation frequencies close to the main resonance. An analytical expression that relates the nonlinear behavior of the device to its geometry and material properties is derived. Amplitude-frequency (A-f) and third-order intermodulation (IMD3) measurements on 1-GHz AlN CMRs are employed to demonstrate the theoretical reasoning. The two experiments confirm the validity of the analytical derivation when the system is dominated by thermally induced nonlinearities. In the case of large frequency difference between the modulation frequencies, purely elastic nonlinearity can also be extracted from the IMD3 measurements.

High power and low temperature coefficient of frequency oscillator based on a fully anchored and oxide compensated ALN contour-mode MEMS resonator

This paper reports on the design and experimental verification of the first high power and low temperature coefficient of frequency (TCF) oscillator based on a fully anchored and temperature compensated AlN contour-mode MEMS resonator operating at 950 MHz. Full anchoring of the AlN resonant body is introduced as an innovative design to improve the device linearity without altering the resonator quality factor. The enhanced power handling of the device enabled the implementation of a high power (6 dBm) and low phase noise (-85 dBc/Hz at 1 kHz offset and -172 dBc/Hz floor) oscillator with improved temperature stability (~600 ppm total frequency variation and no phase noise degradation over a 75 °C range).

Analytical and Numerical Methods to Model Anchor Losses in 65-MHz AlN Contour Mode Resonators

This paper presents and experimentally validates two different approaches to describe the quality factor (Q) due to anchor losses in 65-MHz aluminum nitride (AlN) contour mode resonators (CMRs). The first method is an approach that can be considered qualitative in nature, as it consists of a simplified analytical model that assumes quasi-static anchor conditions and a semi-infinite substrate. Despite its simplicity, it effectively provides designers with some guidelines on how to layout resonator anchors. The second approach is quantitative and consists of a numerical technique that can be considered as an alternative to the use of perfectly matched layers (PMLs). The new finite-element method imposes fixed-constraint (FC) boundary conditions at the edges of the released regions, and the Q is calculated as the ratio of strain energy in both resonator and anchors and the total acoustic energy transferred to the substrate. The two approaches (analytical and numerical) are experimentally validated through measurements of 216 AlN CMRs operating at their fundamental resonance frequency (around 65 MHz). The proposed numerical approach is also compared with the results obtained using PML. This comparison shows that the FC technique has a similar accuracy to PML in predicting Q, but it is superior to the latter when reflections from the clamped boundaries become relevant.

Sub-milliwatt integrated oven for temperature stable laterally vibrating piezoelectric MEMS resonators

This paper reports the design and demonstration of an integrated oven for aluminum nitride (AlN) piezoelectric MEMS resonators that enables device heating from -40°C to +85°C with a power consumption as low as 368μW - the lowest ever recorded for MEMS resonators. The same resonators exhibit quality factors (Q) as high as 4,459. In this work, RF power delivery is decoupled from resonator supporting beams, hence alleviating the trade-off between power consumption and Q-factor; moreover, heaters are placed externally to the resonator body, hence eliminating the deleterious effects of serpentines on the acoustic properties of the device. More importantly, this ovenization technique is independent of the resonator geometry, so it is broadly applicable to any resonator frequency (70MHz to 1.16GHz in this work). This demonstration constitutes a fundamental stepping stone in enabling temperature stable oscillators with extremely low power consumption.

Impact of metal electrodes on the figure of merit (k t 2 ·Q) and spurious modes of contour mode AlN resonators

This paper presents an experimental study on the impact of the metal electrodes on the level of the first spurious mode, electromechanical coupling (kt2) and quality factor (Q) of laterally vibrating AlN contour mode resonators (CMRs). Pt, Ni, and Al are selected for the fabrication of the device top electrode since they exhibit a broad range of values of Youngs modulus, density and resistivity, which are the most relevant parameters that have an impact on the electromechanical characteristics of the device. The results on the level of the first spurious mode, and kt2 suggest that the acoustic mismatch between electrode and nonelectroded regions affect mostly these parameters. The extracted Q (after subtracting the effect of the electrode resistance) exhibits a trend in line with the theory of interfacial dissipation.

Nonlinear lumped electrical model for contour mode AlN resonators

This paper presents a lumped electrical model to simulate the nonlinear behavior of aluminum nitride contour mode resonators. The model is derived from the Duffing equation and validated through experiments. Amplitude-frequency (A-f) and third order intermodulation distortion (IMD3) measurements were performed to extract an equivalent nonlinear coefficient α. The two experiments yield the same results when the system is dominated by thermally-induced nonlinearities. In case of high frequency modulations, purely mechanical non-linearity can also be extracted.

Damping directly impacts flicker frequency noise of piezoelectric aluminum nitride resonators

This paper presents an analysis on the effect of damping on flicker frequency (1/f) noise of 1.1 GHz aluminum nitride (AlN) contour mode resonators (CMR). A total of 52 different AlN-CMRs are systemically designed and fabricated to give quality factors (Q) ranging from 300 to 3500, allowing the study of how two major damping mechanisms in AlN-CMRs, 1) anchor losses and 2) thermoelastic damping (TED), affect the resonator 1/f noise. In total, we have measured 104 CMRs and the results confirm that 1/f noise shows a clear power law dependence that is close to 1/Q3, independently of the main nature of the damping mechanism. Understanding and accounting for the effect of damping on 1/f noise is crucial for building ultra-low noise Microelectromechanical systems (MEMS) resonators for sensing, timing, and frequency applications.