A Temperature-Stable Piezoelectric MEMS Oscillator Using a CMOS PLL Circuit for Temperature Sensing and Oven Control

Abstract

In this paper, design, analysis, and implementation of a piezoelectric microelectromechanical systems (MEMS) oscillator on an ovenized microplatform is presented. An oxiderefill process is used to compensate the first-order temperature coefficient of frequency of MEMS resonators, as well as to realize thermal isolation structures. The technology enables fabrication of low-power ovenized device fusion platforms using standard silicon on insulator wafers. Utilizing the intrinsic frequencytemperature characteristic of two MEMS resonators, temperature sensing and closed-loop oven-control is realized by phaselocking two MEMS oscillators at an oven-set temperature. The design of the phase-lock control loop is studied using multidomain linear models. Control loop dynamics, noise properties, and nonideal effects are analyzed. Low-power and low-noise phaselocked loop-based control circuitry is designed in 0.18-µm CMOS to interface with the MEMS resonators. Using the developed technology, an oven controlled MEMS oscillator exhibits an overall frequency drift of <8 ppm over −40°C to 70°C without the need for system calibration. In addition, the MEMS oscillators exhibit near zero phase noise degradation in closedloop operation.[2015-0023]

Micromachined Resonators: A Review

“…Alternatively, some other temperature compensation techniques rely on dual resonator devices that have different temperature coefficients and are placed in a thermal feedback loop. These attain frequency stabilities of ±1 ppm over −20 °C to 80 °C in [ 206 ], and of ±4 ppm from −40 °C to 70 °C in [ 207 ], and interestingly do not require calibration, which is a significant advantage in order to reduce device cost. However, these techniques require heating of the resonators, and thus will consume higher amounts of current that are on the order of a few milliamps.…”

“…Direct thermal tuning can also be used to control the resonator’s frequency and improve its frequency stability, similarly to oven controlled crystals [ 243 , 244 , 245 ]. Other approaches involve the use of phase-locked loops in arrangements that can include mismatched temperature coefficient resonators that result in a temperature stable operating point (e.g., [ 207 , 208 ]) or that can include temperature to digital converters that control the output frequency of the loop to compensate the resonator temperature variance (e.g., [ 203 , 206 , 207 , 246 , 247 ]). More recently, the use of electronics for compensation has precluded MEMS oscillators from operating at power budgets that rival that of quartz oscillators.…”

Concepts and Key Technologies of Microelectromechanical Systems Resonators

“…This means that a resonator with temperature stability at room temperature can be obtained by designing the inversion point. An extended mode MEMS resonator based on an oxide refilling process was proposed and reported in [93]. The first order TCF of the extended mode MEMS resonator can be compensated more effectively by placing silicon dioxide islands in high strain regions, resulting in a TCF of 4 ppm/K.…”

Enhancing Micro-Oven Power and Stiffness in Encapsulated Devices for Timing Reference Applications

“…To achieve the high frequency stability required for MEMS sensors in industrial applications, temperature compensation methods are essential. Previous work has shown that a combination of passive and active temperature compensation methods can achieve the frequency stability required in timing reference applications [1][2][3][4][5][6][7][8][9][10][11]. Active temperature compensation can be achieved using a resistor or micro-oven embedded within the device layer, which heats only the suspended resonating element that is thermally isolated within the die [1,[3][4][5].…”