History of Crystal Oscillator Origins

Ⅰ.Preface
As a core frequency control component, crystal oscillators are widely used in industrial equipment, security and surveillance equipment, medical devices, automotive electronics, smart home devices, and other fields. From a macro perspective, the construction of global information infrastructure is intrinsically linked to the development of crystal oscillators. This article will systematically analyze the technological evolution of crystal oscillators, from the discovery of the piezoelectric effect to nanoscale packaging, revealing how they have propelled human technological progress through four industrial revolutions.

Ⅱ.The Development History of Crystal Oscillators

1. The Technological Enlightenment Period of Crystal Oscillators

In 1880, brothers Jacques and Pierre Curie, while studying quartz crystal plates, discovered that applying mechanical stress to the crystal would generate a displacement of electrical charge, proposing the concept of the piezoelectric effect.

Principle of the Piezoelectric Effect: If pressure is applied to a piezoelectric material, it generates an electric potential difference (known as the direct piezoelectric effect). Conversely, applying a voltage generates mechanical stress (known as the inverse piezoelectric effect). When the pressure takes the form of a high-frequency vibration, it produces a high-frequency electrical current. Conversely, when a high-frequency electrical signal is applied to a piezoelectric ceramic, it generates a high-frequency acoustic signal (mechanical vibration), which is what we commonly refer to as an ultrasonic signal.

1918: Paul Langevin researched the use of plates cut from quartz crystals to develop an early sonar system for submarine detection.

Sonar System Principle: It organically integrates various sonar functions to comprehensively process information and enable centralized control, meeting diverse tactical requirements. Its main functions include noise direction finding, echo ranging, sonar pulse detection, target identification, and torpedo alert. In this work, Langevin used X-cut quartz plates to generate and detect sound waves in water.

1921: Professor Walter G. (WG) Cady of Wesleyan University patented the quartz crystal oscillator.
For this patent, he utilized a quartz crystal resonator to control the frequency of an oscillator. He also described the use of quartz bars and plates as frequency standards and filters. Therefore, Cady is commonly recognized as the first person to use a quartz crystal to control the frequency of an oscillator circuit.

1923: Professor G. W. Pierce of Harvard University developed a crystal oscillator circuit that placed the crystal between the grid and the anode of a valve/vacuum tube. This was the predecessor to the Pierce oscillator configuration.

1925: Westinghouse Electric installed a crystal oscillator as the master oscillator for their radio station KDKA. Van Dyke developed the equivalent circuit of the quartz crystal resonator. The equivalent circuit of a quartz resonator exhibits two resonant frequencies: one is the series resonant frequency (fS), which is the frequency at which the Lg, Cg, Rg branch resonates. The other is the parallel resonant frequency (fP), which is the resonant frequency of the entire equivalent circuit. Since Cg < C0, these two frequencies are very close. The reactance-frequency characteristic of the quartz resonator can be derived from its equivalent circuit. Between fS and fP, the circuit exhibits inductive reactance; outside this region, it exhibits capacitive reactance.

1926: Y-cut crystals were first discovered and utilized. Until this point, X-cut quartz crystals had been the only form used. It was discovered that while the temperature coefficient of X-cut crystals was approximately -20 ppm/°C, that of Y-cut crystals was approximately +100 ppm/°C. This indicated that different crystal cut orientations could exhibit different temperature coefficients

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1928: Warren Marrison (Bell Telephone Laboratories, though note: the 1928 date for Marrison's clock is more accurate than the 1950s parenthetical) developed the first quartz crystal clock. Quartz clocks replaced precision pendulum clocks as the world's most accurate timekeepers (until atomic clocks).
Principle of the Atomic Clock: Atomic clocks measure time based on the electromagnetic waves emitted when atoms absorb or release energy. The timing mechanism of an atomic clock achieves such precision that it may deviate by only 1 second in 20 million years. Currently, atomic clocks are the world's most accurate timing instruments.

1934: The AT-cut and BT-cut quartz crystal resonators first appeared. These cuts were discovered independently by Lack, Willard, and Fair in the USA; Koga in Japan; and Beckmann and Straubel in Germany.

2. The R&D Period: Achieving Mass Production of Crystal Oscillators

1950: The atomic clock was developed. Quartz clocks achieved a maximum accuracy of 1 second in 30 years (approx. 30 ms/year). Bell Laboratories developed a hydrothermal process for growing quartz crystals on a commercial scale.

1956: Synthetically grown quartz became widely available.

The Development Period: Batch Production, Scaling, and Shift from Military to Civilian Use

1968: Juergen Staudte of North American Aviation invented the photolithographic process for manufacturing quartz crystal oscillators. This enabled them to be made small enough for use in portable products like wristwatches.

1970: Nearly all crystals used in electronic products were synthetic.
1976: The first SC-cut crystals became available. They are primarily used in oven-controlled crystal oscillators (OCXOs) because they exhibit the optimal temperature coefficient at the operating temperatures of these OCXOs.

3. The Rapid Development Period: Diversification of Electronic Products and Applications

From 1990 to the present: Over the past 30+ years, the development direction of quartz crystal oscillators has shifted from DIP packages to SMD (Surface Mount Device) packages with smaller sizes. Packaging has transitioned from traditional metal cans to encompass plastic, metal, and ceramic encapsulations. Precision and operating frequencies have increased significantly, demanding increasingly refined manufacturing processes. Applications have expanded from single-use domains to today's diverse scenarios, including 5G, IoT (Internet of Things), automotive electronics, smart healthcare, and intelligent home appliances.

III. Summary

The over 70 years from 1880 to 1956 marked the initial period of quartz crystal oscillators. This era witnessed the emergence of numerous innovative talents and a continuous stream of profoundly influential inventions. The development of quartz crystal oscillators to their current state has taken many years. Technological progress cannot be achieved overnight; it is a gradual process of understanding, discovery, and maturation.