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 fundamental concepts of crystals and crystal oscillators, while also exploring the manufacturing processes of both 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 lead to confusion. In general, a "crystal" refers to a passive component, typically known as a "Crystal" in English. It requires an external capacitor to initiate oscillation. On the other hand, a "crystal oscillator" is an active device, commonly referred to as an "Oscillator" in English. It does not require an external capacitor and provides a clock signal as soon as it is powered on.

Second, the manufacturing process of quartz crystals.

Quartz crystal oscillators go through multiple complex steps, including cutting, grinding, silver plating, dispensing, and nitrogen filling. However, this process comes with several risks:

1. Fragility: Due to the high precision required, quartz wafers must be very thin, making them prone to breaking during handling and transportation.
2. Quality inconsistency: High temperatures, such as during soldering, can cause adhesives to loosen, resulting in defective products.
3. Air leakage: The sealing of the metal housing is critical for maintaining accuracy. If not properly sealed, air leakage can occur, leading to oxidation and significant frequency deviation.

As a result, 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 use standard semiconductor manufacturing techniques, with both the die and packaging being fully automated. This approach effectively eliminates many of the issues 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 extreme conditions.
2. Excellent quality consistency: With a DPPM as low as 0.15, they offer exceptional reliability and performance consistency.
3. High precision: Most MEMS silicon crystals include internal temperature compensation circuits, ensuring stable performance across a wide temperature range.

The Sitime MEMS silicon crystal is fully compatible with traditional quartz crystals and can be directly substituted without any changes to the circuit design.