IEC 62047-29:2017 pdf download

IEC 62047-29:2017 pdf download.Semiconductor devices – Micro-electromechanical devices – Part 29: Electromechanical relaxation test method for freestanding conductive thin films under room temperature
1 Scope
This part of IEC 62047 specifies a relaxation test method for measuring electromechanical properties of freestanding conductive thin films for micro-electromechanical systems (MEMS) under controlled strain and room temperature. Freestanding thin films of conductive materials are extensively utilized in MEMS, opto-electronics, and flexible/wearable electronics products. Freestanding thin films in the products experience external and internal stresses which could be relaxed even under room temperature during a period of operation, and this relaxation leads to time-dependent variation of electrical performances of the products. This test method is valid for isotropic, homogeneous, and linearly viscoelastic materials.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 62047-2:2006, Semiconductor devices – Micro-electromechanical devices – Part 2: Tensile testing method of thin film materials IEC 62047-3:2006, Semiconductor devices – Micro-electromechanical devices – Part 3: Thin film standard test piece for tensile testing IEC 62047-8:201 1 , Semiconductor devices – Micro-electromechanical devices – Part 8: Strip bending test method for tensile property measurement of thin films IEC 62047-21 :201 4, Semiconductor devices – Micro-electromechanical devices – Part 21: Test method for Poisson’s ratio of thin film MEMS materials IEC 62047-22:201 4, Semiconductor devices – Micro-electromechanical devices – Part 22: Electromechanical tensile test method for conductive thin films on flexible substrates
3 Terms and symbols
3.1 Terms and definitions For the purposes of this document, the following terms and definitions apply.3.1 .1 gauge factor G F ratio of the relative change in electrical resistance R to the change in mechanical strain (Δε) Note 1 to entry: Gauge factor is defined as G F = (ΔR/R)/ Δ ε , where ΔR is the change in resistance, R is the unstrained resistance, Δ ε is the change in the mechanical strain. R and ΔR are expressed in ohms and Δε in μm/m. 3.1 .2 piezoresistive coefficient π ratio of the relative change in electrical resistivity ρ , to the change in applied mechanical stress Note 1 to entry: Piezoresistive coefficient is defined as π = (Δ ρ / ρ )/Δ σ , where Δ ρ is the change in resistivity, ρ the unstressed resistivity, Δ σ the applied mechanical stress. Stress is expressed in Pascal [Pa]. 3.2 Symbols and designations The shape of a test piece and symbols are presented in Figure 1 and Table 1 , respectively. The overall shape of the test piece is similar to a conventional thin film or sheet test piece for strip bending test (see IEC 62047-8:201 1 ), and it has a freestanding structure and four electric contacts for electrical measurements.
4 Test piece
4.1 General A test piece shall be prepared using the same fabrication process as the target film of an actual MEMS device. Shaping the test piece shall be performed to prevent formation of cracks, flaws, or delamination in the test piece. 4.2 Shape of a test piece The shape of a test piece is shown in Figure 1 . Because the change in electrical resistance is related to strain or stress, electrical resistance shall be measured in a region of uniform strain. The electrical resistance shall be measured using four wire method, and this requires four electric contacts on the test piece. To eliminate the effect of the fixed boundary near the grips, the gauge length (l 1 ) shall be at least 20 times larger than the width (l 2 ). The width shall be more than 1 0 times the thickness (h). 4.3 Measurement of dimensions Gauge length (l 1 ), width (l 2 ), and thickness (h) should be measured with an error of less than ± 5 %. The thickness should be measured according to Annex C of IEC 62047-2:2006 and in Clause 6 of IEC 62047-3:2006.