These materials exhibit particularly advantageous intrinsic properties that can be changed through an applied electric field.
They are usually used for their electro-optic or piezoelectric properties.
These materials are a subclass of the piezoelectric materials family which also exhibit pyroelectric properties. The sign of a ferroelectric material is the polarization hysteresis cycle according to the applied electric field.
Currently, ferroelectric materials are extensively exploited in microelectronics thanks to their dielectric properties which can be adjusted with changes to the material’s chemical composition or even the material's shaping.
Some materials have their optical properties changed when they are subjected to a static or time-varying electric field. This is called electro-optical effects.
There are two types of electro-optical effects:
- First, there is the linear electro-optic effect in which the index variation is proportional to the applied electric field. This is called Pockels effect, named by Friedrich Pockels who discovered it in 1893.
- Then, there is the quadratic electro-optical effect, wherein the index variation is proportional to the square of the electric field. John Kerr discovered it in 1875 by studying optically isotropic areas such as liquid or gasses.
The change in the optical properties of these materials allows control (using an electrical signal) over the polarization, the amplitude and the phase of an optical beam passing there through. This control capability is directly related to the material properties involved, which are defined by a tensor. Depending on the system geometry, one of the coefficients of this tensor will become predominant. The higher the coefficient will be, the greater the electro-optic effect will be important for a given voltage.
The main raw materials used for their electro-optical properties are Lithium niobate (LiNbO3), BBO, KTP and RTP.
But we can find other materials with significantly higher properties which allow to drastically reduce the control voltages or component dimensions. However, these materials can't handle process temperatures greater than 80 °C. That’s why, until now, these materials were only used in a Research & Development context. These materials include SBN single crystals, KTN, and the PLZT type of opto- ceramics.
Crystal Device’s patented technology now overcomes this operating limitation, and allows to produce customized components, tailored to our customer's needs.
Piezoelectricity is the property of certain bodies to electrically polarize themselves under a mechanical stress action. The piezoelectric materials have two types of operation:
- Piezoelectricity direct effect: the property of some bodies to electrically polarize themselves under a force action: some loads appear on the crystal faces.
- Piezoelectricity inverse’s effect: the crystal is deforms when we apply an electric voltage to it.
The materials most used for their piezoelectric properties are quartz, topaz, tourmaline and the ceramics of perovskite crystal structures (PZT).
Quartz is one of the most used materials because when it's subjected to an electrical voltage, it vibrates at a very stable and well-defined frequency. That’s why, thanks to this property, quartz is widely used in watches and clock manufacturers: by applying a voltage to the quartz from a stack, it vibrates and allows the measurement of time.
The PZT types of ceramics are also widespread in many applications such as pressure sensors or lighters.
There are also materials with much higher properties than the traditional ceramics, as well as for optical applications, which allow either better movement on the same voltage, or the generation of more current for the same applied effort.
It can be noted from these: the single crystals PMN-PT or the PZNT-PT ceramics.