Monolithic AlN MEMS-CMOS resonant transformer for wake-up receivers

Abstract

Abstract-A monolithic piezoelectric MEMS-CMOS resonant transformer that can be used in ultra-low-power high-efficiency RF sensing applications is presented for the first time. The MEMS-CMOS resonant transformer is based on a 59 MHz 2-port Aluminum Nitride (AlN) Contour Mode Resonator (CMR) bonded to a 0.18 µm NMOS-based rectifier for voltage boosting and RF-to-DC conversion. The integrated device is fabricated in a foundry-based process by conductive eutectic wafer bonding. To amplify the voltage, the AlN CMR is designed to attain a large quality factor (Q=900) and a relatively low dielectric capacitance (C0=1.51 pF) in relation to the number of rectifier stages (n=20). As a result, a ten-fold voltage gain MEMS-CMOS resonant transformer is demonstrated in this work.

Optimized Resonators for Piezoelectric Power Conversion

“…The I 2 R loss in the motional branch is dependent on the RMS current in the resonator and can be computed based on the sum the charge transferred per cycle, the operating frequency, and the resonator motional resistance, R m . Based on (3)(4)(5) and the values provided in Table II the peak amplitude of the sinusoidal current in the motional branch, I m and the loss in the motional branch, P m can be expressed as:…”

“…Three piezoelectric materials hold significant promise for power conversion: Lead Zirconate Titanate (PZT) ceramics, Lithium Niobate, and Aluminum Nitride [29], [30], [31], [4]. In Table III we compare the properties of these three materials 2 .…”

“…This represents an upper bound for kt under the optimal boundary conditions. Aluminum Nitride has a low mechanical loss but a low k 2 t , its main advantage is that it can be deposited as part of a CMOS compatible process flow, allowing for a high degree of integration with IC processes [4], [29].…”

“…When operated around resonance, piezoelectric resonators can provide a net-inductive impedance with very low loss, replacing the need for magnetics. Piezoelectric resonators also have integration advantages as they can be fabricated with CMOS compatible processes and do not produce fringing magnetic fields which can interfere with sensitive circuits [4]. Taking into account both power dissipation and intrinsic material limits, the upper bound on power density for piezoelectric resonators exceeds what is achievable with discrete components [5].…”

Transverse Spurious Mode Compensation for AlN Lamb Wave Resonators

“…Piezoelectric microelectromechanical (MEMS) resonators offer fascinating prospects for frequency selection, control, and sensing applications thanks to its small size and low resonance impedance. Among various piezo-MEMS resonators, AlN Lamb wave resonators (LWRs) recently capture attention since they enjoys both advantages of surface acoustic wave (SAW) devices and film bulk acoustic resonators (FBARs): the multi-frequency and CMOS-compatible ability [1]- [16]. For all Lamb wave modes propagating in an AlN plate, the S 0 and S 1 mode stand out for their excellent transduction efficiency [17], [17]- [24].…”