FBAR Resonator Sacrificial-Layer Release for Precise Piezoelectric Thinning

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Solution Overview

Problem

Existing methods for manufacturing bulk wave acoustic resonators with suspended thin piezoelectric layers face difficulties in achieving precise thinning and decoupling from the substrate, particularly with techniques like ion implantation/fracture, which are complex and limited in thickness range.

Innovation Solution

A method involving the use of a sacrificial layer to form and then remove, allowing for the creation of a partially suspended thin layer of piezoelectric material between electrodes, enabling the production of bulk wave devices like FBARs with improved decoupling and frequency control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If ion implantation/fracture technique is used to thin the piezoelectric layer, then very small thicknesses (less than 0.5 μm) can be achieved, but the process becomes complex and is limited to specific thickness ranges

Engineering Contradiction:

Improvelayer thickness precisionVSAvoidmanufacturing process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

A sacrificial layer is deposited on the piezoelectric layer before assembly, creating a predefined thickness reference that simplifies subsequent bonding and eliminates the need for complex ion implantation thinning processes

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The sacrificial layer acts as an intermediary element between the piezoelectric layer and the substrate, enabling precise thickness control and facilitating the bonding process without requiring direct thinning of the piezoelectric material

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If the piezoelectric layer is thinned below one micron, then FBAR resonators can be manufactured, but maintaining uniformity in thickness during thinning becomes very difficult

Engineering Contradiction:

Improvethickness uniformityVSAvoidthin layer fabrication difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The sacrificial layer is deposited with a controlled thickness before assembly, establishing a uniform thickness reference that guides the thinning process and ensures consistent final dimensions without requiring difficult post-assembly thinning operations

Inventive Principle:

Principle #10Preliminary action

3Reliability

If a stiffening material is used to ensure transfer above cavities, then the transfer process can be stabilized, but the material must be removed afterwards adding process steps

Engineering Contradiction:

Improvetransfer process stabilityVSAvoidprocess steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The sacrificial layer is temporarily introduced to enable stable transfer and bonding operations, then systematically removed through etching processes, allowing the cavity structure to be formed without requiring permanent stiffening materials

Inventive Principle:

Principle #34Discarding and recovering

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach simplifies the manufacturing process by enabling precise control over layer thickness and decoupling, resulting in resonators with enhanced filtering capabilities and higher bandwidth, overcoming the limitations of previous technologies.

Implementation Method 1

removing the sacrificial layer so as to release said thin layer of piezoelectric material and said first electrode and define the bulk wave resonator

Methodology Applied

Scientific EffectChemical etching:

Implementation Method 2

electromechanical devices exploiting the generation of acoustic waves in thin piezoelectric layers

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentEP2330737B1Method for manufacturing an acoustic resonator with FBAR body waves

Publication Date: 2012.06.20 COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES

Figure 1a~1b
Figure 2a~2c
Figure 2d~2e

AI summary

The method involves depositing a sacrificial layer at a surface of a thin layer of a piezoelectric material (10) and of a lower electrode (12) for defining an assembly. The assembly is assembled with a substrate (20). An upper electrode (21) is formed on a face of the thin layer, where the face is arranged opposite to another face with the lower electrode. The sacrificial layer is eliminated so as to release the piezoelectric material thin layer and the lower electrode and to define a film bulk wave acoustic resonator. A planarization layer (14) is formed on the sacrificial layer. The piezoelectric material is formed of niobate lithium, lithium tantalate or quartz. The sacrificial layer is made of a polymer type material or silicon oxide or metal e.g. titanium, tungsten or molybdenum. The elimination step of the sacrificial layer is performed by etching in acid solution e.g. hydrofluoric acid, phosphoric acid or xenon fluoride solution. The intermediate layer between the piezoelectric material thin layer and the sacrificial layer is formed of tanium nitride or aluminum nitride. The substrate is made of a material such as lithium niobate, lithium tantalate or quartz. The upper and lower electrodes are made of metal such as platinum, molynum, aluminum, copper, tungsten, chromium or alloy of copper and aluminum or an alloy silicon and aluminum or ruthenium.