GB/T 44514-2024 Micro-electromechanical system (MEMS) technology - Four-point bending test method for interfacial adhesion energy of layered MEMS materials
1 Scope
This document specifies a four-point bending test method for measuring interfacial adhesion energy of the weakest interface in the layered micro-electromechanical systems (MEMS) based on the concept of fracture mechanics.
The total thickness of the thin film layers should be 100 times less than the thickness of a supporting substrate (typically a silicon wafer piece).
2 Normative references
There are no normative references in this document.
3 Terms, definitions, symbols and designations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
energy release rate
G
strain energy per unit surface area, which is released during the incremental growth of a crack
Note: The energy release rate can be regarded as the crack driving force, and its unit is given in J/m2.
3.1.2
interfacial adhesion energy
GC
critical energy release rate at the moment of crack extension
Note: Its unit is given in: J/m2.
3.2 Symbols and designations
The shape of the test piece and the symbols are presented in Figure 1 and Table 1, respectively. The overall shape of the test piece is similar to a sandwiched cantilever beam, and it should have a pre-crack or a notch for crack initiation. After initiation of the crack, the crack follows the weakest interface in the layered materials system.
4 Test piece
4.1 General
The test piece for the layered MEMS materials shall be prepared using the same fabrication process that applies to actual MEMS devices. Machining of the test piece shall be performed to prevent formation of unintended cracks or flaws and delamination in the test piece.
4.2 Shape of a test piece
The overall shape of a test piece is shown in Figure 1. Because the evaluation of the energy release rate relies on several simplifying assumptions, the geometric shape of the test piece should be designed as follows: the thickness of the test piece should be 50 times less than the length and width of the test piece, and the length should be 10 times larger than the width. The total thickness of the layered materials should be 100 times less than the thickness of a supporting substrate. A pre-crack or notch shown in Figure 1 is machined using conventional ways like a diamond saw, laser ablation, or chemical etching. This pre-crack initiates cracking in the supporting substrate under bending, and after that the cracking leads to the introduction of an interface crack between two adjacent layers of the weakest interface in the layered materials.
4.3 Measurement of dimensions
To analyze the test results, the test piece dimensions shall be accurately measured because the dimensions are used to determine the mechanical properties of test materials. Spacing between the pins (L), width (b), and thickness (h) should be measured with an error of less than ±5 %.
4.4 Evaluation of energy release rate
The energy release rate (G) is evaluated using the following Equation (1):
