Design and preparation method of PMUT with isolation trench

Design and preparation method of a pmut with isolation trench

technical field

1. The present invention relates to the technical field of pmut, in particular to a design and preparation method of a pmut with an isolation trench.

Background technique:

2. MEMS technology is a micro-scale mechatronics system technology developed in recent decades. Based on mems technology, the researchers designed and fabricated a micromachined ultrasonic transducer. Compared with traditional ultrasonic transducers, it has the advantages of miniaturization, integration, high performance and low cost, and has become one of the important research directions of ultrasonic transducers. According to the working principle, mut can be divided into capacitive micromachined ultrasonic transducers and piezoelectric micromachined ultrasonic transducers. cmut usually requires a high DC bias voltage to meet high transmit and receive sensitivity, which causes some difficulties for circuit design and integration and device fabrication. cmut usually requires a high DC bias voltage to meet high transmit and receive sensitivity, which It causes certain difficulties for circuit design and integration and device manufacturing. Compared with cmut, pmut does not require high voltage to obtain high sensitivity, and has little influence of parasitic capacitance, low power consumption, and is easy to integrate with cmos circuits. The basic principle of pmut is mainly the piezoelectric effect. When the piezoelectric crystal is deformed by applying an external force in a specific direction, positive and negative opposite charges will be generated on the two opposite surfaces of the crystal, which is called the positive piezoelectric effect; and when an electric field is applied in the crystal polarization direction, it will cause The crystal is deformed, and the crystal returns to its original shape after removing the electric field. This phenomenon is called the inverse piezoelectric effect. When pmut is used as a transmitter, the voltage between the upper and lower electrodes causes the piezoelectric layer to have an inverse piezoelectric effect, which generates high-frequency vibration and then radiates ultrasonic waves; when used as a receiver, the sound pressure acts on the piezoelectric layer, resulting in deformation. Due to the positive piezoelectric effect Causes an electrical signal to be generated between the upper and lower electrodes. The basic structure of pmut is a typical suspended film structure, the piezoelectric layer is between the top and bottom electrode layers, and the bottommost substrate is generally an insulating substrate silicon (silicon-on-insulator, soi). The insulating layer is usually silicon dioxide (sio2). The main function in the working process is the suspended film structure composed of the top electrode, the piezoelectric layer, the bottom electrode layer and the insulating layer.

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