A tunable ferroelectric based unreleased RF resonator

This paper introduces the first tunable ferroelectric capacitor (FeCAP)-based unreleased RF MEMS resonator, integrated seamlessly in Texas Instruments’ 130 nm Ferroelectric RAM (FeRAM) technology. The designs presented here are monolithically integrated in solid-state CMOS technology, with no post-processing or release step typical of other MEMS devices. An array of FeCAPs in this complementary metal-oxide-semiconductor (CMOS) technology’s back-end-of-line (BEOL) process were used to define the acoustic resonance cavity as well as the electromechanical transducers. To achieve high quality factor (Q) of the resonator, acoustic waveguiding for vertical confinement within the CMOS stack is studied and optimized. Additional design considerations are discussed to obtain lateral confinement and suppression of spurious modes. An FeCAP resonator is demonstrated with fundamental resonance at 703 MHz and Q of 1012. This gives a frequency-quality factor product $$f \cdot Q = 7.11 \times 10^{11}$$ which is 1.6× higher than the most state-of-the-art Pb(Zr,Ti)O3 (PZT) resonators. Due to the ferroelectric characteristics of the FeCAPs, transduction of the resonator can be switched on and off by adjusting the electric polarization. In this case, the resonance can be turned off completely at ±0.3 V corresponding to the coercive voltage of the constituent FeCAP transducers. These novel switchable resonators may have promising applications in on-chip timing, ad-hoc radio front ends, and chip-scale sensors. A reinvention of memory technology from Texas Instruments has enabled the creation of high-efficiency, high-quality resonators. Microscopic radio frequency (RF) resonators vibrate at stable frequencies, a property that can be used in tracking time, communicating, sensing, and imaging. Technological advances are demanding smaller, more power-efficient and cost-effective components, but traditional resonators are reaching their theoretical limits. Dana Weinstein and her team from the United States’ Purdue University and Texas Instruments have developed a new resonator integrated into existing chip fabrication with no post-processing, and offers much higher quality factor than alternate devices made side by side with electronic circuits. In this new paper, the team discusses the optimization that produced these low loss vibrations, and how the resonance can be manipulated by adjusting the electric polarization of the device.