Polycrystalline diamond micro-electromechanical systems (MEMS) for passive micro-rheology and sensor applications

[摘要] Owing to its unique mechanical and electrical properties, diamond is an attractivecandidate for use in micro-electro-mechanical systems (MEMS) devices. This thesispertains to the development, fabrication and characterisation of polycrystallinediamond (PCD) micro-electromechanical systems (MEMS) devices for passivemicro-rheology and sensor applications. Intrinsic PCD and boron doped PCD (BDD)materials are investigated.Micro-rheology is the study of soft matter rheological properties, often performedby observing interactions with mechanical devices, such as micro-cantilevers, atthe micro scale. In order to overcome significant fluid dampening, these devicesare actuated at or around their resonant frequency, and several measurementsare taken at different frequencies to build a data set. We present an intrinsicdiamond-based micro-cantilever micro-rheometer device, the passively actuatedthermal fluctuations of which can be characterised in a fluid at least up to theviscosity of water (8.90 × 10−4 Pa.s ). A possible data analysis method to extract afluid’s viscoelastic properties from the power spectrum of the thermalfluctuations of a device submerged in the fluid is also presented. This methodnegates the requirement for measurements at multiple actuation frequencies andprovides useable data up to the sample rate of the data acquisition system.Intrinsic PCD cantilevers for passive micro-rheology were fabricated from polished(~3 nm Ra) 500 nm thick PCD on Silicon <100> substrate films. Cantileverdimensions range from 5 μm to 150 μm in length and 1 μm to 4 μm in width, thehighest height/width/length ratio cantilevers yet reported. PCD samples werepatterned using electron beam lithography and highly anisotropic diamond etchingwas achieved using an RIE Ar/O2 plasma etching method. A new fabricationprocess to minimize cantilever undercut is presented. The thermal fluctuations ofthe free-standing cantilever structures in air and water at room temperature weresuccessfully captured by a laser Doppler vibrometer system. Resonant frequenciesof devices are presented, ranging from 38 – 554 kHz in air and 42 – 148 kHz inwater, comparable to that of similar single crystal diamond devices.Polycrystalline Diamond MEMS for Passive Micro-rheology and Sensor Applications iiPCD micro-cantilevers have been investigated extensively in different sensorapplications. Recently, boron-doped diamond micro cantilevers exhibitingpiezoresistive behavior have been fabricated from multi-layer PCD material. Wepresent a boron-doped PCD micro-cantilever piezoresistive sensor fabricated froma single layer of BDD thin film on silicon. BDD material was electricallycharacterised and found to be electrically stable for up to at least 60 secondswithin the I/V ranges investigated. BDD micro-cantilevers were fabricated frompolished (~3 nm Ra) 480 nm thick BDD on Silicon <100> substrate films. The Ushapedcantilever’s dimensions ranged from 60 μm to 110 μm in length with legs4 μm in width. The deflection sensitivity of the fabricated cantilever devices isreported, ranging from 0.029 mΩ/Ω-μm to 0.063 mΩ/Ω-μm. An analysis of thenature of the piezoresistive mechanism in the BDD devices is presented.

[发布机构] University:University of Glasgow;Department:School of Engineering

[关键词] MEMS, diamond, polycrystalline, micro-rheology, silicon, dry etch, wet etch, etching, resonators, viscosity, cantilever, micro-cantilever, boron doped diamond, piezo, piezoresistive.