## 2 Background and Motivation  
The development of RF MEMS technology is critical to advancing global telecommunications infrastructure and defense capabilities. Hence, the integration of capacitive and piezoelectric transduction mechanisms within a single hybrid MEMS resonator represents a potential technological leap forward. This is due to the need to overcome the inherent limitations of single-transduction systems in terms of frequency agility, port-to-port isolation, susceptibility to spurious modes, power efficiency, and miniaturization. The hybrid MEMS resonators combine the high-quality factors and low spurious mode susceptibility of capacitive transduction with the low insertion loss (strong electromechanical coupling coefficients) of the piezoelectric one, thus holding the potential to improve the overall device performance.  
Moreover, the Internet of things (IoT), ubiquitous wireless sensors, and smart city devices require sophisticated communication protocols, which underscore the growing importance of on-chip MEMS technologies in providing critical solutions for intelligent, ubiquitous, and low-power applications [17]. This work aims to position hybrid MEMS resonators as central components in future RF systems by offering an alternative solution to the current technologies, including both capacitive and piezoelectric resonators, which benefits from its unique ability to seamlessly consolidate the advantages of two transducer technologies into one standalone resonator. In particular, we focus on addressing the issue of parasitic feedthrough, which is a key challenge in MEMS resonators. Feedthrough suppression is crucial since it allows the desired resonance signal to be detected easily from the background noise. Both capacitive and piezoelectric resonators have employed various techniques to decrease feedthrough levels in prior works, such as differential measurement techniques [18], dummy twin designs [19], and the use of peripheral electrodes [20]. However, these methods often require additional complexity in device structure, circuit-level trick, fabrication technique, and measurement scheme.  
Conversely, the hybrid resonator device studied in this work, which operates on a two-port scheme, inherently exhibits low feedthrough levels without imposing additional design complexity. This makes our device not only competitive in terms of feedthrough levels to all prior works, but also potentially desirable in terms of simplicity and effectiveness when compared to existing technologies. Also, this low-feedthrough characteristic makes the proposed device configuration well suited as a sensing element in applications like MEMS gyroscopes [21] and local oscillators with a MEMS tank circuit [22], where high feedthrough can be detrimental from a signal-to-noise ratio perspective. The hybrid MEMS resonator scheme achieves low feedthrough levels inherently, thus offering a streamlined solution for low-parasitic operation, while retaining the overall performance. This innovation holds exceptional promises for microsystem applications, where feedthrough mitigation is crucial for key device functionality. It is anticipated that these devices hold unique abilities to offer superior performance with enhanced frequency control and stability, better noise characteristics, and greater efficiency. Ultimately, this could lead to more reliable and robust RF front-end systems [1; 2; 4; 7; 8; 9; 10; 16], while enabling emerging applications in wearable technology, flexible electronics, and advanced sensor networks [23; 24; 25; 26; 27]. The newly investigated hybrid resonator configuration could pave the way for MEMS resonator technologies to evolve and meet the increasingly stringent demands of modern and future wireless communication technological landscapes.