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piezo_mems-related-terminology

Piezo

What is ‘piezo’?

A piezo refers to a piezoelectric element/device that generates a voltage when force is applied (piezoelectric effect) or, conversely, is deformed when voltage is supplied (reverse piezoelectric effect).

[Piezo Effect]

Piezo elements utilize piezo materials that exhibit the piezoelectric effect. When force is applied, the position of the positive (+) and negative (-) ions move, creating a charge bias that generates voltage.

[The Principle of Electrical Polarization] / [Voltage Generation via Electrical Polarization]

The piezoelectric effect is primarily used in sensors, while the reverse piezoelectric effect is often adopted in actuators.

Piezo Material Types

Piezo materials can roughly be classified into single crystal, ceramics, thin-film, and other types.

[Piezo Materials]

ROHM utilizes thin-film piezos comprised of lead zirconate titanate (PZT).
Taken from the initials of the element symbol PbZrxTi1-xO3 (O<x<1), PZT plays a major role in piezoelectric devices by providing excellent piezoelectric performance.

Thin-Film and Bulk Piezo

Generally, elements with a thickness on the order of several μm are classified as thin-film piezo (piezoelectric thin-film), while those in the tens of μm are considered bulk piezo (thick-film piezo).
Utilizing thin-film piezo allows users to achieve greater miniaturization and integration along with higher performance and lower power consumption.

Thin-Film PZT Deposition Methods

Thin-film PZT deposition is achieved through various methods including sol-gel, sputtering, and MOCVD. The features of each are summarized in the table below.

 Sol-Gel MethodSputtering MethodMOCVD Method
 A sol-gel liquid is applied to the substrate, heated, then baked to form a film. This process is repeated multiple times to obtain the desired thickness.High energy Ar ions are made to collide with a target, causing target material to be ejected and attach to a substrate, forming a film.Metal organic materials are put in the chamber and a film is formed by a chemical reaction. The film thickness can be controlled on the atomic layer order.
Piezoelectric Performance◎◎?
Throughput△〇×
Reliability◎△〇
Uniformity◎〇〇
Polarization Stability△〇△
Cost△△△
ApplicationsActuator (1～3μm)Actuator or Sensor
(1～5μm)		FeRAM (<100nm)

ROHM's thin film piezo MEMS foundry provides total support from prototyping, development to mass production to realize small, energy-saving and high-performance products by combining our advanced thin film piezo and LSI microfabrication technology and abundant mass production experience.

>　Thin-Film Piezo MEMS Foundry (Services)

The next page contains a brief summary of piezo-related terminology.

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