Temperature-compensated aluminum nitride lamb wave resonators

Abstract

In this paper, the temperature compensation of AlN Lamb wave resonators using edge-type reflectors is theoretically studied and experimentally demonstrated. By adding a compensating layer of SiO2 with an appropriate thickness, a Lamb wave resonator based on a stack of AlN and SiO2 layers can achieve a zero first-order temperature coefficient of frequency (TCF). Using a composite membrane consisting of 1 microm AlN and 0.83 microm SiO2, a Lamb wave resonator operating at 711 MHz exhibits a first-order TCF of -0.31 ppm/degrees C and a second-order TCF of -22.3 ppb/degrees C(2) at room temperature. The temperature-dependent fractional frequency variation is less than 250 ppm over a wide temperature range from -55 degrees C to 125 degrees C. This temperature-compensated AlN Lamb wave resonator is promising for future applications including thermally stable oscillators, filters, and sensors.

Thermally compensated aluminum nitride Lamb wave resonators for high temperature applications

“…The thermal compensation technique using a compensating layer of SiO 2 to a device structure has been applied to many different kinds of resonators. [7][8][9][10][11][12][13] This present work demonstrates the thermal compensation for AlN Lamb wave resonators operating at high temperature using an AlN/SiO 2 composite structure. By designing composite structures with different normalized AlN thickness ͑h AlN / ͒ and normalized SiO 2 thickness ͑h SiO 2 / ͒, Lamb wave resonators with a zero first-order temperature coefficient of frequency ͑TCF͒ at 214°C, 430°C, and 542°C are experimentally demonstrated.…”

“…The metalized interface significantly enhances the electromechanical coupling coefficient because a strong electric field can be induced between the IDT electrodes and the metalized interface. [11][12][13][14] Aluminum ͑Al͒ is often used as the electrode material for the bottom electrode and the IDT. However, the Lamb wave resonators are designed to operate at high temperature up to 700°C so Al is not preferred due to its low melting point of 660°C.…”

“…The mismatch is likely due to the neglect of the bottom electrode and IDT as well as the neglect of the film stresses in the calculation. 13 In addition, the accuracy of the first-order TCF prediction relies heavily on the accuracy of the material property data. However, the material data at high temperature might differ considerably from the data at room temperature.…”

High-Q aluminum nitride Lamb wave resonators with biconvex edges

“…Among various micro-electro-mechanical resonator technologies, aluminum nitride (AlN) Lamb wave resonators utilizing the lowest symmetric (S 0 ) mode have demonstrated the most promising technology for ultimately realizing this vision. [1][2][3][4][5] Recently, the robust temperature compensation of AlN Lamb wave resonators by using one layer of silicon dioxide [6][7][8] or highly doped silicon (Si) 9 has been demonstrated.…”

AlN thin films grown on epitaxial 3C–SiC (100) for piezoelectric resonant devices

“…For example, piezoelectric AlN thin films have been used to fabricate a variety of radio frequency ͑RF͒ resonators and filters, such as layered surface acoustic wave ͑SAW͒ devices, 1,2 thin film bulk acoustic resonators, 3 contour mode resonators, 4 and Lamb wave resonators. 5,6 These devices are enabled by the high acoustic velocity, high electromechanical coupling coefficient, and chemical inertness of AlN thin films. However, due to limitations in material properties, AlN-based resonators have some natural drawbacks, such as a lower quality factor ͑Q͒ in comparison to quartz-based resonators.…”