What Is a MEMS Oscillator?
A MEMS oscillator is an oscillator that generates a clock signal source essential to electronic devices using a MEMS-structured resonator.
While quartz crystal devices have been commonly used for oscillators in the past and are still used in many cases today, MEMS oscillators utilize a thin-film microfabrication process technology called MEMS (micro-electro-mechanical systems) structure for resonance points.
A MEMS oscillator is characterized by its ability to be used in small timing devices, excellent resistance to shock and vibration, and high reliability. MEMS oscillators are highly regarded compared to conventional timing devices.
Uses of MEMS Oscillators
MEMS oscillators are used in various electronic devices that require timing and clock signals. Specific applications include a wide variety of electronic devices such as cell phones, PCs, wearable devices, automotive-connected devices, and medical equipment.
With the introduction of 5G in recent years, which has led to higher line speeds and the rise of IoT, the market for automatic driving and VR devices is also expected to expand, and shipments are expected to grow markedly in the future.
The Principle of MEMS Oscillators
The principle of MEMS oscillators is that the resonator of the oscillator is made of MEMS, a thin-film microfabrication technology, and the resonator is made of single-crystal silicon with tensile strength 14 times greater than that of titanium.
Unlike quartz devices, which use the piezoelectric effect for a piezoelectric drive, the MEMS resonator is driven by electrostatic excitation forces, and the MEMS oscillation circuit and the MEMS resonator are electrically connected, and a total oscillation maintenance circuit is activated to keep the MEMS resonator mechanically fixed at a certain frequency. The MEMS resonator can be made to oscillate at a fixed frequency.
Compared to crystal oscillators, MEMS oscillators can be set to any frequency using a phase-locked loop (PLL). On the other hand, there are some drawbacks, such as increased power consumption due to more complex circuit configurations, and noise characteristics that are easily degraded due to frequency jumps.
Other Information on MEMS Oscillators
1. Comparison of Temperature Characteristics With Crystal Oscillators
The basic structure of a crystal oscillator is a combination of a crystal unit and an ASIC oscillator circuit. In this case, the temperature sensor used to correct the temperature characteristics of the oscillator is built into the ASIC.
Therefore, compared to a MEMS temperature sensor that can be formed on the same chip, the change in oscillation frequency concerning temperature change may be larger.
MEMS oscillators not only have the advantage of small changes in oscillation frequency with temperature change but also have the advantage of small mass and small characteristic fluctuation due to vibration.
2. Noise Characteristics
Noise characteristics of oscillators are a very important factor in ensuring good application characteristics. In particular, crystal oscillators have the advantage over MEMS oscillators in that the crystal structure itself is very simple, making it easy to obtain low noise characteristics.
However, compared to MEMS oscillators, crystal oscillators are more prone to jitter during vibration due to their larger mass. Therefore, depending on the application environment, MEMS oscillators may be more suitable in terms of noise characteristics.
3. Frequency Deviation
While MEMS oscillators are less cost-effective than competing ceramic oscillators and other types of oscillators, they can ensure excellent oscillation frequency stability. The frequency deviation of general ceramic oscillators is as large as about 1%, which limits the applicable applications, while MEMS oscillators can achieve frequency deviation as low as on the order of ppm.