Self-referencing microelectromechanical systems (mems) resonator with dual …

Description (excerpt)

CROSS-REFERENCE TO RELATED APPLICATIONS Pursuant to 37 C.F.R. § 1.78(a)(4), this application claims the benefit of and priority to prior filed co-pending Provisional Application Ser. No. 63/661,206, filed Jun. 18, 2024, and is a continuation-in-part of co-pending Utility patent application Ser. No. 18/503,804, filed Nov. 7, 2023, which claimed priority to expired Provisional Application Ser. Nos. 63/382,730 filed Nov. 8, 2022, 63/383,963 filed Nov. 16, 2022, and 63/486,312 filed Feb. 22, 2023, each of which is expressly incorporated herein by reference in its entirety. RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. FIELD OF THE INVENTION The present invention relates generally to microelectromechanical systems and, more particularly, to self-referencing microelectromechanical systems with dual mechanical modes for temperature-independent environmental sensing. BACKGROUND OF THE INVENTION Piezoelectrically transduced microscale resonant devices have diverse applications, including inertial sensing, radio frequency (RF) signal processing, and environmental monitoring. Microelectromechanical systems (MEMS) resonators may be ideal for low-power, compact, and cost-effective sensing due to their small size and low power consumption. These microscale piezoelectric resonators can be extensively employed for frequency filtering, sensing, and clock generation within these fields. They can cover a broad frequency range and actuate various vibrational modes, such as extension, thickness, shear, and flexure, while achieving high selectivity, narrow bandwidth, and excellent stability. As handheld and Internet of Things (IoT) devices continue to shrink, the lightweight, low-power, high-frequency range, and multimode capabilities of micro- and nano-scale resonators have garnered significant research interest. However, manufacture and implementation of microscale resonant devices is not without challenges. For instance, certain piezoelectric materials display sputtering deposition temperature requirements that make them unsuitable for deposition in many instances. Moreover, some piezoelectric materials (e.g., lead zirconate titanate (PZT), etc.) contaminate cleanroom environments or equipment or may require a post-deposition poling step. Accordingly, MEMS resonators incorporating different materials in new formations may be required. SUMMARY OF THE INVENTION The present invention overcomes the foregoing problems and other shortcomings, drawbacks, and challenges of microelectromechanical systems. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. To the contrary, this invention includes all alternatives, modifications, and equivalents as may be included within the spirit and scope of the present invention. According to one embodiment of the present invention a self-referencing, microelectromechanical system (MEMS) with dual mechanical modes for temperature independent environmental sensing comprises: a resonator configured to resonate in a first fundamental width extensional mode (1st WEM) and to resonate in a second contour mode (2nd CM), comprising: an input port; an output port; a top electrode comprising an aluminum chromium layer; a silicon-oxide layer; an aluminum-nitride layer; and an RF ground comprising a silicon layer. Upon passing a signal to the top electrode of the resonator, the top electrode and the RF ground establish an electric field to enable transduction through the piezoelectric, aluminum-nitride layer, and the resonator has adjacent contour modes close in frequency such that mechanical resonances of the resonator in differing resonance modes shift together as a function of temperature over a temperature range from −200 C to +200 C, the simultaneous shift of the mechanical resonances remaining constant across the temperature range enabling sensing of various criteria including mass loading, stress, humidity, or chemical interactions. Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, il