P0-15 Temperature Compensated Bulk Acoustic Wave Resonator and its Predictive 1D Acoustic Tool for RF Filtering

Abstract

The design of Bulk Acoustic Wave "BAW" resonators should take into account the stringent requirements of thermal effects. In this paper, we propose a thermal model, allowing the reduction of the Temperature Coefficient of Frequency "TCF" with a slightly modified process while retaining a good coupling and quality factor. For a significant reduction of the TCF, a SiO 2 layer is added above the upper electrode. A TCF of +1.5 ppm/°C was obtained at 2.08 GHz. The present accuracy of the 1D model is approximately 1 ppm/°C. Most material parameters were extracted by comparison between the modeling and the measurement of BAW resonators with different stacks. To improve the dispersion of the TCF, the uniformity of each layer is introduced into the model. Firstly, the reduction of the top SiO 2 Bragg layer thickness dispersion from 2 % to 0.2 % is achieved, using an ion etching. The compensation of BAW resonators in our process has been improving for PCS diversity standard. This model was used to design a Personal Communications Service "PCS" RX diversity filter (1.93-1.99 GHz). The compensated loaded and unloaded resonators were used in the filtering function and present TCFs between 0.8 and -7 ppm/°C with a coupling factor of approximately 5.2 %.

Sources of Third–Order Intermodulation Distortion in Bulk Acoustic Wave Devices: A Phenomenological Approach

“…In addition to being able to calculate the temperature oscillations, we also need to determine how these oscillations influence the device performance. For the specific case of BAW devices, there is consensus in assuming that the detuning of BAW devices with temperature is due to the variation of multiple material properties with temperature (Lakin et al, 2000;Ivira et al, 2008;Petit et al, 2007). We reflect this in our model by adding a temperaturedependent term to the stiffened elasticity in (1)…”

Temperature compensated BAW resonator and its integrated thermistor for a 2.5GHz electrical thermally compensated oscillator

“…In this paper, we use an one-chip sensor in molybdenum which surrounds the BAW resonator. The applied temperature in the thermal chamber was the same in the region of the BAW resonator [6]. A dispersion of approximately ±3 is measured for each temperature.…”

“…On top of the stack, the passivation layer allows adjustment of the targeted frequency by locally removing material with an ion etching (as called: Gas Cluster Ion Beam). The stacking of the BAW resonator is defined thank to the predictive thermal 1D Mason model [6] with the temperature coefficient of elasticity measured by picoseconds ultrasonic's experiment [7]. An uncompensated BAW resonator with an acoustic mirror in one quarter of a wavelength occurs a low quality factor of approximately 550 (Figure 4).…”

Performance of BAW resonators at cryogenic temperatures

“…Each additional part per million (ppm) in the Temperature Coefficient of Frequency (TCF) has a big impact on the filter's mask and thus affects the signal quality. To this regard, many thermal models have been presented to cover the current commercial temperature range [1] [2], but still no measurements have been presented down to cryogenic temperatures for Aluminum Nitride (AlN) BAW resonators working at GHz frequencies [3].…”