Hantianxia breaks the monopoly of RF front-end market

Nowadays, the domestic RF front-end industry environment is favorable, and the government, capital and society have given great support and attention. Suzhou Handianxia has successfully broken the market monopoly of international giants. Its core products are bulk acoustic wave filter chips and RF modules based on MEMS technology, which have been widely used in 4G/5G mobile terminals.

Resonators have been widely used in many fields. Bulk acoustic resonators have the advantages of small size, high operating frequency, and compatibility with integrated circuit manufacturing processes. Ideally, a bulk acoustic resonator only excites longitudinal modes in the thickness direction. However, there are also transverse modes in the acoustic resonator, which propagate in the horizontal direction along the surface of the piezoelectric layer, adversely affecting the quality factor of the acoustic resonator. Therefore, there is still a need for an acoustic resonator that at least overcomes the above defects.

To this end, Hantianxia applied for an invention patent entitled "Acoustic resonator, its manufacturing method and a filter including the acoustic resonator" (application number: 202110717075.1) on June 28, 2021, and the applicant was Shenzhen Hantianxia Microelectronics Co., Ltd.

Figure 1 Flowchart of acoustic resonator manufacturing method

FIG1 is a flow chart of the method for manufacturing an acoustic resonator of the present invention, which mainly includes the following steps: first, forming a reflective element inside or on the surface of a substrate (S101); then, forming a seed layer, a lower electrode and a piezoelectric layer overlapping with the reflective element in sequence above the substrate in a vertical direction, wherein the region where the seed layer, the lower electrode and the piezoelectric layer overlap with the reflective element constitutes an effective resonance region (S102); then, etching the piezoelectric layer at one end of the effective resonance region to form a gap (S103); finally, forming an upper electrode and a bridge portion above the piezoelectric layer, wherein the bridge portion covers the gap (S104).

Specifically, the reflective element has the form of a cavity, which can reflect energy, thereby reducing energy loss and improving the quality factor Q of the acoustic resonator. A seed layer, a lower electrode and a piezoelectric layer overlapping the reflective element are formed in sequence above the substrate in the vertical direction, that is, in the y direction. The seed layer and the piezoelectric layer can be made of the same piezoelectric material. The lower electrode and the upper electrode include conductive materials and provide an oscillating electric field along the y direction when electrically excited. The area where the seed layer, the lower electrode, the piezoelectric layer and the upper electrode overlap with the reflective element constitutes the effective resonance area of ​​the acoustic resonator. The piezoelectric layer is etched at one end of the effective resonance area to form a second groove. The second groove extends through the entire thickness of the piezoelectric layer in the y direction. The end of the effective resonance area that is etched to form the second groove is called the connection end, which is connected to the interconnection portion.

The bridge and the gap provide an acoustic impedance mismatch at the boundary of the effective resonance area at the connection end of the acoustic resonator. This acoustic impedance mismatch causes the reflection of the sound wave at the boundary, so that the sound wave is not propagated outside the effective resonance area and thus energy loss is avoided. The bridge and the gap can improve the quality factor Q of the acoustic resonator. In addition, by patterning the upper electrode and the bridge, the termination of the upper electrode at the opposite end to the connection end can terminate the effective resonance area of ​​the acoustic resonator and reduce energy loss by generating an acoustic impedance mismatch. This can also improve the quality factor Q of the acoustic resonator.

In short, Hantianxia's acoustic wave filter patent forms gaps around the effective resonance area of ​​the acoustic resonator without significantly increasing the process complexity, so as to confine the resonance energy to the effective resonance area, thereby reducing the loss of resonance energy and improving the quality factor of the acoustic resonator.

Hantianxia is the first company in China to fully master the mass production technology of bulk acoustic wave filters. The R&D team has mastered all key processes and systematically mastered the relationship between device structure and performance parameters. Hantianxia will continue to promote the development of new products and new technologies to break the constraints of Western countries on the development of my country's high-end integrated circuit industry.