Piezoelectric components

In 1881, Pierre and Jacques Curie demonstrated the phenomenon of piezoelectricity-polarization of certain bodies under stress and vice versa. The first application was in sonar during the First World War, and Cady was the first to use a resonator to stabilize an oscillator in 1918.

The first quartz-controlled commercial radio appeared in 1930. These resonators operated at low frequencies, 10 to 100 kHz in bending modes. Elongation modes operated up to around 200 kHz, and surface shear modes made it possible to reach megahertz. Thickness shear resonators have rapidly reached frequencies of 20 to 30 MHz. In these modes, it's the thickness that determines the frequency, and mechanical machining techniques can produce disks down to 0.03 mm (50 MHz). Polishing techniques have made it possible to operate in harmonic modes, and unconventional machining has made it possible to reduce thickness to around 8 µm (200 MHz) in industrial applications.

Surface wave devices, using waves propagating parallel to the surface of a piezoelectric plate generated from interdigitated metal tracks deposited on this surface at distances of a few micro-meters between them, give access to frequencies between 100 and 1,000 MHz.

Resonators are used for frequency stabilization in oscillators. Depending on the configuration and application, there are simple oscillators (XO Crystal Oscillator), oscillators whose frequency can be adjusted by a voltage (PCF Voltage Controlled Crystal Oscillators), or oscillators whose temperature-dependent frequency variations are compensated (TCXO Temperature Compensated Crystal Oscillator). There are also oscillators that operate the resonator in an oven maintained at a constant temperature (Oven Controlled Crystal Oscillator, OCXO).

This article is aimed primarily at users or future users of resonators and oscillators. We have therefore tried to establish an approach for defining the type of oscillator to be chosen in a piece of equipment, according to the mode of use, based on criteria of frequency stability (as a function of time and environment), coherence between different nodes, or criteria of power consumption, dimensions, or target price...

Volume-wave resonators remain unrivalled, in terms of stability, for frequencies from a few kilohertz (watchmaking applications) up to 250 MHz [and up to 1,000 MHz using integrated PLL (Phase-Lock Loop) structures]. Beyond that, oscillators based on other techniques are used, such as dielectric resonator oscillators (DRO) or surface wave oscillators... Piezoelectric resonator filters are used in radio communications, in SSB (Single Side Band) applications, as noise filters or channel filters... The overvoltage characteristics of these resonators...