Research on the Formation Mechanism of Ordered Wrinkles Induced by Piezo-driven Microprobe

Author:Sun Yi

Supervisor:chen ben yong

Database:Doctor

Degree Year:2019

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Pages:122

Size:11159K

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With the development of micro-nano manufacturing technology,the design and manufacture of Micro-Electro-Mechanical System(MEMS)are gradually developing to the nanometer scale.Therefore,higher requirements are put forward for the performance and reliability of the micro-structures and micro-devices that make up the MEMS systems.In the manufacturing process of many micro-structures and micro-devices(such as mecro-gears,micro-sensors and microfluidic chips),it is an important research direction to fabricate micro and nano structures and devices with multilayer structures of film and substrate.Therefore,the performance and reliability of such structures or devices depend on the physical and chemical properties of both the film and the substrate.The mechanical instability of the stiff film structure on the compliant substrate often causes microscopic wrinkling.For those irregular and uncontrollable wrinkling patterns,which are formed spontaneously,often lead to the failure of the function of the micro and nano structures and devices.And for those comtrollable and ordered wrinkle patterns,which play an important role in improving the performance of the micro and nano structures and devices.Therefore,it is of great scientific significance to study the changes of microscopic topography caused by the interaction between the film and the substrate for improving the performance of the micro and nano structures and devices.In this dissertation,a method based on piezo-driven microprobe is proposed for inducing the localized wrinkling of metal film/compliant substrate.The local compressive stress field in the film can be adjusted in real time by precisely controlling the displacement of the probe,thus the real-time tuning of the wrinkling morphology can be realized.The formation mechanisms and dynamic evolution processes of radial and circumferential wrinkles in the metal film/compliant substrate under out-of-plane indentation and in-plane displacement are studied in detail.The main research work and innovations of this dissertation are summarized as follows:1.The research status of the localized wrinkling in the metal film is analysed in detail,including the wrinkling in the metal film/compliant substrate and metal film/viscous substrate,the ways to control different wrinkle patterns and the tunning mechanisms of the wrinkling morphology.The research goal and content of this thesis are proposed.2.Based on the wrinkling and fracture mechanisms of the stiff film on the compliant substrate,the formation and evolution of the wrinkles and cracks in an Au film/PDMS substrate under thermal stress are analysed.The formation mechanism of locally ordered wrinkle patterns in the stiff film/compliant substrate is described.The experimental results show that the surface defects can change local compressive stress state of the film,thus altering the local wrinkling morphology.3.A method based on piezo-driven microprobe is proposed to induce the localized wrinkling of the metal film/compliant substrate,and an experimental setup for forming localized wrinkles is constructed.By precisely controlling the displacement of the probe to apply continuous out-of-plane indentation and in-plane displacement to the initially smooth Au film/PDMS substrate,the localized wrinkling and fracture of the film are induced,and the formation and morphological evolution of the wrinkles and cracks can be tuned in real time.The in-situ monitoring of the wrinkle evolution is achieved by using an optical microscopy to monitor the evolution of the film surface morphology in real time.The formation mechanisms,the morphological characteristics and the evolution laws of the localized wrinkles and cracks are studied detailly,which provides experimental basis for manufacturing the real-time controllable wrinkling and fracture patterns.4.The morphological transition of the local wrinkles is achieved by controlling the single probe to apply the out-of-plane indentation and in-plane displacement to the initially wrinkled Au film/PDMS substrate.The experimental results show that the local wrinkles will evolve into radial patterns under the out-of-plane indentation,while they will evolve into the circumferential patterns under the in-plane displacement.The transition degree and morphology of the wrinkles can be tuned by controlling the the displacement magnitude and loading direction of the probe.The experimental method and results have some guiding significance and engineering application value for regulating some unsatisfactory wrinkling patterns in micro-nano structures,micro-nano devices and engineering materials.5.By controlling the double probes to apply the out-of-plane indentation to the initially wrinkled Au film/PDMS substrate,the morphological transition of the local wrinkles is tuned,and the physical mechanism of ordering for the surface wrinkles between the probes is revealed.The experimental results show that the transition degree of the wrinkle morphology is related to the probe spacing and the indentation depth.The smaller the probe spacing and the greater the indentation depth,the greater the transition degree of the wrinkle morphology and the more ordered the wrinkles will be.The results have important guiding significance for inducing the larger-area and highly ordered wrinkles in the stiff film/compliant substrate with the multi-probe.