Introduction

Crystal units are essential electronic components used in a wide range of devices, including smartphones, automobiles, computers, communication equipment, and IoT devices. A crystal unit generates the precise timing signals required for electronic circuits to operate accurately. In many ways, it functions like a "metronome" inside electronic equipment, maintaining a stable operating rhythm known as a clock signal. Because electronics rely heavily on accurate timing control, the performance of a crystal unit directly affects the stability and reliability of the entire device.

This article explains the basics of crystal units in a simple and easy-to-understand way, including how they work, their structure, the difference between crystal units and crystal oscillators, and the relationship between frequency and quartz blanks. Whether you are new to electronics or looking for a better understanding of crystal technology, this guide provides a simple and clear explanation.

What Is a Crystal Unit? - Basics and Functions

A crystal unit is a passive component that utilizes the piezoelectric properties of quartz to vibrate at a highly stable frequency. When combined with an oscillation circuit, this stable vibration is used to generate the "rhythm" (clock signal) that serves as the reference timing for electronic circuits.

Typical applications include:

• Generating operation timing for electronic device control circuits (microcontrollers)
• Frequency reference sources for communication equipment
• Clock and timer circuits

A constant and accurate rhythm is essential for electronic devices to operate correctly, and crystal units play a central role in providing this timing reference.

How Does a Crystal Unit Work?

The operating principle of a crystal unit is based on the piezoelectric effect of quartz crystal.

Quartz has two important characteristics:

• Applying mechanical pressure to quartz generates electrical voltage (Piezoelectric Effect)
• Applying electrical voltage to quartz causes it to deform and vibrate (Inverse Piezoelectric Effect)

Because of these properties, quartz can convert electrical energy into mechanical vibration and mechanical vibration back into electrical energy.

Piezoelectric Effect

When mechanical force or pressure is applied to quartz crystal, electrical charges appear on the crystal surface.

Inverse Piezoelectric Effect

When voltage is applied to quartz crystal, the crystal physically deforms and vibrates.

When an AC voltage is applied to a quartz crystal, the crystal expands and contracts in response to the voltage changes, producing vibration. Quartz also possesses a characteristic called resonance, enabling it to vibrate efficiently at a specific frequency. The resulting resonant frequency is highly stable and accurate.

Because of these characteristics, crystal units provide the following benefits:

• Extremely small frequency deviation
• Stable operation over long periods
• Low susceptibility to temperature changes

These stable vibrations support the accurate operation of electronic circuits.

In addition, a crystal unit continues to vibrate at a constant frequency through the repeated interaction of the piezoelectric effect and the inverse piezoelectric effect. The vibration characteristics of a quartz blank are determined by the way the crystal is cut, known as the crystal cut. These unique vibration characteristics are referred to as vibration modes.

The two most common vibration modes are thickness-shear vibration and flexural vibration. A typical example of a crystal unit that utilizes thickness-shear vibration is the AT-cut^*1 crystal unit. In contrast, tuning-fork crystal units are a representative example of devices that utilize flexural vibration.

Thickness-Shear Vibration

AT-cut^*1 Crystal Unit

When an electrical voltage is applied, the opposite surfaces of the quartz plate move in opposite directions, producing thickness-shear vibration.

Vibration ))) Frequency Range (Several MHz to Several Hundred MHz)

※1: An AT-cut is a quartz crystal blank cut at an angle of approximately 35°15′ relative to the Z-axis of a synthetic quartz crystal. It is the most widely used crystal cut for crystal units and crystal oscillators.

Flexural Vibration

Tuning-Fork Crystal Unit

When an electrical voltage is applied, the tines of the tuning-fork-shaped quartz element flex, generating flexural vibration.

Vibration ))) Frequency Range (kHz Band, e.g., 32.768 kHz)

Discovery of Quartz's Electrical Properties - From Gemstone to Electronics -

Quartz has long been valued for its transparency and brilliant appearance, making it a popular material for gemstones, ornaments, and ceremonial objects throughout history. The French physicists the Curie brothers were the first to discover that this beautiful mineral possesses remarkable electrical properties.

In 1880, Pierre Curie and Jacques Curie discovered that applying mechanical force to crystals such as quartz, tourmaline, topaz, and Rochelle salt generates electricity. This phenomenon became known as the piezoelectric effect.

The term "Piezo" is derived from the ancient Greek word piezein, meaning "to press" or "to squeeze," and describes the phenomenon in which electricity is generated by applied pressure.

The piezoelectric effect was later applied to electronic technology and evolved into the crystal units used today. Crystal units have since become one of the fundamental technologies supporting modern electronics, including communication equipment and computers.

Pierre Curie is also well known for receiving the 1903 Nobel Prize in Physics together with his wife, Marie Curie, for their pioneering research on radioactive materials.

Conclusion

A crystal unit is an electronic component that utilizes the piezoelectric effect to convert electrical energy into mechanical vibration and vice versa, producing highly stable oscillation at a specific frequency. Its exceptional stability is supported by the resonant characteristics of quartz, which naturally vibrates at a precise frequency, as well as its extremely low frequency deviation. Thanks to these characteristics, crystal units play a vital role as the timing reference for electronic devices.

Quartz, once appreciated primarily as a gemstone throughout history, has become an indispensable material in modern electronics and continues to support a wide range of advanced technologies today.