Introduce crystals and crystal oscillators and compare the process of quartz crystal oscillator with MEMS silicon crystal oscillator

This article provides an overview of the basic concepts of crystals and crystal oscillators, with a focus on the working principles of quartz crystal oscillators and MEMS silicon crystal oscillators, along with a comparison of their key parameters.

First, let's clarify the difference between a crystal and a crystal oscillator.

In China, the terms "crystal" and "crystal oscillator" are often used interchangeably, which can cause confusion. In general, a "crystal" refers to a passive component, known as a "Crystal" in English. It requires an external capacitor to start oscillation. On the other hand, a "crystal oscillator" is an active device, called an "Oscillator" in English. It does not need an external capacitor and produces a clock signal as soon as it is powered on.

Second, the manufacturing process of quartz crystals.

Quartz crystal oscillators go through numerous steps such as cutting, grinding, silver plating, dispensing, and nitrogen filling. However, this process comes with several challenges:

1. Fragility: Due to the high precision required, quartz wafers must be very thin, making them prone to breaking during transportation.
2. Inconsistent quality: High temperatures, such as during soldering, can cause the adhesive to loosen, leading to defective products.
3. Air leakage: The accuracy of the oscillator depends heavily on the silver plating. If the metal casing is not properly sealed, air leakage may occur, causing oxidation and significant frequency deviation.

Because of these issues, the DPPM (Defective Parts Per Million) for quartz crystals typically ranges from 200 to 300, indicating a relatively higher defect rate.

Third, the production process of MEMS silicon crystals.

MEMS silicon crystal oscillators are manufactured using standard semiconductor processes, with both the die and packaging being fully automated. This approach effectively eliminates many of the risks associated with traditional quartz crystals:

1. High shock resistance: These devices can withstand up to 50,000G of shock, making them highly durable even under harsh conditions.
2. Excellent quality consistency: With a DPPM as low as 0.15, meaning only 0.15 defects per million units, they offer superior reliability.
3. High precision: Most MEMS silicon crystals include internal temperature compensation circuits, ensuring accurate performance across a wide temperature range.

The Sitime MEMS silicon crystal is fully compatible with quartz crystals and can be directly replaced without any modifications to the circuit design. This makes it an ideal upgrade option for systems requiring improved stability and reliability.