Multilayer piezoelectric element and its manufacturing method

Abstract

A multilayer piezoelectric element excellent in durability comprises a multilayer body and external electrodes. The multilayer body has an active portion which is formed by alternating at least one piezoelectric body and internal electrodes including first and second internal electrodes and expands / contracts depending on the voltage applied between the first and second internal electrodes. The external electrodes are formed on two side surfaces of the multilayer body. One of the external electrodes is connected to the first internal electrode, and the other is connected to the second internal electrode. Each external electrode is composed of three or more layers including a first layer in contact with the side surface of the multilayer body and a second layer formed on the first layer.

Description

technical field [0001] The present invention relates to a multilayer piezoelectric element (hereinafter also simply referred to as "element"), for example, to a fuel injection device mounted in an automobile engine, a liquid injection device such as an ink jet, a precision positioning device such as an optical device, or a vibration prevention device, etc. Drive elements in combustion pressure sensors, shock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensitive sensors, yaw rate sensors, etc., and sensor elements mounted in piezoelectric gyroscopes, piezoelectric switches, piezoelectric Multilayer piezoelectric elements used as circuit elements in electric transformers, piezoelectric circuit breakers, etc. Background technique [0002] Conventionally, a multilayer piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately laminated is known as a multilayer piezoelectric element. Multilayer piezoelectric actuato...

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Problems solved by technology

[0013] First, since the active layer undergoes repeated dimensional changes during driving, when driving continuously for a long period of time under high electric field and high pressure, the external electrode and the piezoelectric body may peel off, or the external electrode itself may be cracked. Contact failure may occur at the connection between the external electrode and the internal electrode

Therefore, voltage cannot be supplied to some piezoelectric bodies, and if used for a long time, the displacement characteristics will change, sparks will be generated, and the drive will stop.

[0014] In recent years, small multi-layer piezoelectric elements have been driven continuously for a long period of time by applying a higher electric field in order to obtain a large displacement. Therefore, such a problem has become apparent.

[0015] In addition, in the inert layer disclosed in Patent Document 3, although the shrinkage difference between the active layer and the inert layer is alleviated, when a high voltage is applied, especially in the case of continuous driving for a long time, the electrodes forming the inert layer 62 Cracks occur at the interface between 61 and the piezoelectric layer (active part) 63, and there is a problem in durability

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