BAW filter structure and preparation method thereof

Abstract

The invention discloses a BAW filter structure and a preparation method, and relates to a radio frequency filtering technology. In order to solve the problem that industrial production cannot be realized due to the stress problem in the prior art, the scheme is provided, and mutually independent piezoelectric film units are generated on the surface of an epitaxial substrate to obtain a transfer structure body; arranging a resonance area on the supporting substrate and covering the bonding unit to obtain a bonding structure body; the upper surface and the lower surface of the transfer structure body are overturned, and the bottom electrode units and the resonance areas are bonded in a one-to-one correspondence mode to obtain a BAW structure body; the epitaxial substrate is removed, and a top electrode unit is generated on the surface, making contact with the epitaxial substrate originally, of the piezoelectric film unit. The single crystal thin film device has the advantages of being simple in structure, simple in process, high in isolation degree and extremely small in stress problem, low in cost, high in efficiency and high in yield during batch production, and suitable for being applied to industrial production and especially suitable for industrial manufacturing of the single crystal thin film device.

Description

technical field [0001] The invention relates to radio frequency filtering technology, in particular to a BAW filter structure and a preparation method. Background technique [0002] RF filter is one of the important devices in the field of wireless communication. With the advent of the era of big data and the Internet of Things, the filters assembled in the RF front-end must develop in the direction of high frequency, low loss, miniaturization, and integration. Bulk Acoustic Wave (BAW) filters based on piezoelectric materials are a preferred solution for RF filters. By cascading multiple BAW resonators according to a certain topology, the center frequency can be as high as several GHz. RF filter specifications. Compared with traditional ceramic filters and surface acoustic wave filters also based on piezoelectric materials, BAW filters have unparalleled volume advantages, as well as advantages such as high operating frequency band and high power capacity. [0003] The bas...

AI Technical Summary

Problems solved by technology

However, these methods all perform wafer bonding and substrate peeling of the piezoelectric film, which have the following disadvantages: (1) The thermal expansion coefficient mismatch between the piezoelectric film and the substrate is one of the main reasons for the stress of the film. The variable is determined by the public expression ΔL=α·ΔT·L, where α is the coefficient of thermal expansion, ΔT is the temperature change, and L is the length. It can be seen that the warpage and stress of the film are proportional to its size

The warpage and stress of the piezoelectric film bonded to the whole wafer are relatively large. During the substrate peeling and subsequent device processing, it is very easy to cause the collapse and damage of the resonant structure, resulting in a high failure rate of the device.

(2) Whole wafer bonding has high requirements on the flatness of the support substrate surface, so chemical mechanical polishing has to be used, which has high process complexity and is easy to cause surface mechanical damage.

(3) Cascade construction of filters usually requires interconnecting the bottom and top electrodes of multiple BAW resonators, using the method of whole wafer bonding. Later, it is necessary to etch the piezoelectric film to form interconnection holes. Difficult and easy to cause collapse and damage of the film

[0006] Considering parameters such as stress, length, thickness, temperature, etc. in the laboratory, it is not impossible to produce chips in a refined manner, but there will be great problems in applying laboratory methods to industrialized industries.

None of the above methods can achieve the rapid mass production and high yield required by industrialization

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