This paper presents a compact 213 GHz fundamental oscillator with an optimal embedding network that maximizes the output power. Fabricated in 65-nm bulk CMOS, the oscillator occupies a core area of only 70×40 pm2, owing to the use of a compact low-loss capacitive transformer structure. The oscillator achieves 0.56-mW output power while consuming a DC current of 14.35 mA from a 1-V power supply, representing a recording-breaking DC-to-RF efficiency of 3.9% amongst fundamental oscillators above 200 GHz.

This paper reports an approach to designing compact high-efficiency millimeter-wave fundamental oscillators operating above the fmax/2 of the active device. The approach takes full consideration of the nonlinearity of the active device and the finite quality factor of the passive devices to provide an accurate and optimal oscillator design in terms of the output power and efficiency. The 213-GHz single-ended and differential fundamental oscillators in 65-nm CMOS technology are presented to demonstrate the effectiveness of the proposed method. Using a compact capacitive transformer design, the single-ended oscillator achieves 0.79-mW output power per transistor (16μm ) at 1-V supply and a peak dc-to-RF efficiency of 8.02% (VDD=0.80 V) within a core area of 0.0101 mm2, and a measured phase noise of -93.4 dBc/Hz at 1-MHz offset. The differential oscillator exhibits approximately the same performance. A 213-GHz fundamental voltage-controlled oscillator (VCO) with a bulk tuning method is also demonstrated in this paper. The measured peak efficiency of the VCO is 6.02% with a tuning range of 2.3% at 0.6-V supply.

Wake-up receivers have been proposed to provide continuous sensing in a wide variety of Internet of Things applications. To achieve impedance transformation and passive amplification between the antenna and rectifier node, current wake-up receivers employ large magnetic transformers that exhibit both low Q and inductance per unit area in planar CMOS technology. The adoption of piezoelectric MEMS resonators to replace magnetic transformers offers an area-efficient, high-Q, monolithic solution that allows large voltage amplification for ultra-low-power applications. AlN Contour Mode Resonators (CMRs) are an emerging class of piezoelectric MEMS that offers frequency reconfiguration via lithography.

A new wake-up receiver (WuRx) designed in 0.13 μm CMOS process is hybrid-integrated with a micro-electromechanical system (MEMS) RF resonator. While only consuming 166 nW of power (18.8 nW for the comparator and 147 nW for periphery), the WuRx is capable of detecting RF signals as weak as -60 dBm. In order to achieve this sensitivity, a passive voltage-boosting network comprised of a high quality factor (high-Q) piezoelectric MEMS resonator is utilized, in place of an inductor, to amplify the received voltages applied to a CMOS rectifier. The output of the rectifier is then applied to a low-power comparator used to set a logical bit that indicates when an RF signal has been detected. The trade-offs in designing the voltage boosting network are explained and an equation for the optimum number of rectifier stages is derived.

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=1150) 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.