Design and Characterization of MEMS Oscillator for Micro Power Generators

What is a MEMS oscillator?

A resonator within the MEMS oscillatorvibrates in response to electrostatic or piezoelectric stimulation from the analogue driver IC. MEMS oscillators have excellent durability and low power consumption, and they can generate frequencies ranging from 1 Hz to hundreds of MHz.
By convention, integrated circuits (ICs) that provide a solitary production frequency are called oscillators. MEMS oscillators have extra electronics to control or set their production frequencies in addition to MEMS resonators, sustaining amps, and other components. Stage-protected loops, which generate selectable or programmable productivity frequencies from the upstream MEMS reference frequencies, are frequently a part of these circuits.

High-performance MEMS applications:

A computer network’s high-speed connections need perfect clock synchronization. Two well-known synchronization technologies are Synchronous Ethernet (SyncE) and Accuracy Period Procedure, which are included in IEEE 1588.
These standards demand that each system’s local oscillators produce a precise, stable reference even in the presence of varying external variables, such as temperature changes. The favoured option has been oven-controlled quartz crystal oscillators (OCXO). However, they are often huge and power-hungry.
Today, high-performance MEMS devices may be found to satisfy these strict criteria. They achieve this by including advanced features like temperature correction. For instance, Dual MEMSTM technology with two MEMS resonators on a single chip is used in SiTime’s Super TXCO devices.
The second resonator servesas an incredibly precise temperature sensor, while the first resonator is built for a flat frequency response across temperatures. Due to their intimate thermal coupling, only 100 m separates the resonator and temperature sensor.
The resonators collaborate with a fractional-N PLL that is exceptionally precise to achieve better than 0.1 ppb resolution with incredibly low noise.

Effectiveness of MEMS Oscillators:

Early MEMS resonators lacked the stability to serve as time references; however, modern devices can achieve stability down to 5ppm. Low-power devices can achieve a frequency tolerance of 20ppm and a stability of 100ppm for portable usage.
The MEMS oscillatorcan survive high levels of stress and vibration because of the use of semiconductor packing, which is especially useful in portable and wearable electronics like digital cameras, mobile phones, and watches that are always at risk of being dropped.

Using MEMS Oscillators in Design:

Designers should adhere to best practice layout principles for a high-frequency clock device, such as reducing trace lengths, paying attention to routing, minimizing interconnect usage, and utilizing ground planes.

Additionally, capacitors may be useful in several ways when used properly.

Decoupling:

The power supply can be heavily strained by fast-switching devices like clock oscillators, which could lead to voltage sag. A decoupling capacitor next to the power supply can function as a local reservoir to guarantee that there is always enough charge available.

Bypassing:

To reduce the amount of noise that permeates the system, low-impedance channels that shunt this transient energy to the ground must be provided using bypass capacitors.

Power Supply Noise Reduction:

In most applications, a simple 0.1 F capacitor will shunt most of the power supply noise to the ground when placed between the power supply voltage and the power return. Designers can use RC or LC power supply filtering techniques for enhanced noise reduction.

MEMS oscillator For Lowering EMI:

The need to maintain electromagnetic compatibility (EMC) between devices is growing as processor speeds rise and more devices are squeezed into smaller places.
An error or malfunction might occur when a signal from one device couples to another. Because it is frequently extensively dispersed throughout the system and is composed of a repeated square wave with high-frequency harmonics, the oscillator clock is frequently a significant source of electromagnetic interference (EMI).
Good designing techniques, shielding, and filtering can reduce EMI, but they cost more and take up more board area. An alternative method for reducing clock noise is to change the frequency of the clock over time gradually. This change decreases the peak spectral energy in both the fundamental and harmonic frequencies.
This decrease aids in FCC certification as well since the peak power within a certain spectrum is used to calculate EMI.
The SiT9003 is a programmable spread-spectrum MEMS oscillator that lowers EMI by modulating its PLL with a 32 kHz triangle wave to change the output’s center frequency. The user can choose the degree of frequency spreading; for example, changing the output frequency between 98MHz and 100MHz can result in an average EMI reduction of 13dB.

Using MEMS Oscillators and MEMS Technology:

Miniature electro-mechanical components with sizes ranging from a few microns to several millimeters may be created using MEMS technology using conventional semiconductor manufacturing techniques, including lithography, deposition, and etching.
To function as a tuner for microelectronic radios, Harvey Nathanson of Westinghouse created the first MEMS device in 1965. MEMS pressure sensors and accelerometers began to be widely employed in the 1990s in products like car airbags and medical respirators, which sparked broad research and helped lower the cost of MEMS technology.
A MEMS resonator is a tiny (0.1mm or smaller) device created to vibrate at high frequencies when electrostatic stimulation is applied. During manufacture, the resonator structure is initially etched on a silicon-on-insulator (SOI) layer.
The trenches are subsequently filled with oxide to planarize the wafer surfaces. To enable electrical connections, contact holes are then created. Finally, hydrofluoric acid dissolves the oxide, resulting in freestanding, vibrating resonator beams.

Conclusion:

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