Study On Micromachining Techniques For Three-Dimensional Microstructures Based On Controlled Scratching By AFM Tip

With the development of nanotechnology, the requirements for micro/nano system, micro/nano scale components and associated products have become more and more. Either the fabrication of MEMS (Micro Electro Mechanical Systems) components, or the manufacturing of micro/nano devices, the machining techniques in micro/nano scale are necessary for these fabrications. However, the conventional methods always are restricted by the control accuracy in some dimension during constructing the microstructure. As a result, only the two-dimensional or quasi-three-dimensional structures can be realized. Moreover, these fabrication methods all have no on-line or on-site measuring abilities. Thus, to construct an ideal method including fabrication and measuring to fabricate the three dimensional microstructure is significant urgent. The invention of scanned probe microscopy technology leads to the considerable progress of nanotechnologies. And now this technology is extensively used to modify the micro world, i.e. that the scanning tip is used as a tool to fabricate the micro structure under the control of the high accuracy AFM(Atomic Force Microscope) system. Moreover, due to the measuring capability for 3D topographies and no special limitations to work piece material and machining condition, this technology is therefore a perfect method to fabricate 3D microstructures.However, based on the commercial AFM system, the fabricated structures are always 2D. This is because there is no precision controlling in the scratching depth. When the scratching is carried out on the AFM system, the control mode between the scratching activation and scratching depth is open loop. As well known, the scratching depth is dependent on the activation, the properties of sample and the equivalent elastic coefficient. And thus, this mode has no access to control the scratching depth accurately.AFM works through an elastic cantilever which can undergo the elastic deformation freely corresponding to the surface topographies. The elasticity enabling of the cantilever results in the difficulty in depth controlling. Therefore, how to realize the scratching and measuring integrated system has been a challenging subject for the fabrication of 3D microstructure via AFM. In terms of the application state based on AFM, a promising way is to design the associated assistant controller and discover the forming rule of scratching depth so as to provide the real time inspection and closed-loop control for the scratching depth. From the viewpoint of the related theory, construction of scratching system and scratching experiments of this technique, the control technology of scratching depth during fabrication of microstructure with AFM is studied in-depth in this thesis. Then the control-enable scratching machining system based on AFM is established by using the means from multi-disciplines. The detailed contents are listed as follows:Through the analyses for the machining process of 3D microstructures by AFM scratching and the application of the theory of material mechanics, the relationship between the scratching depth of the tip and AFM system is analyzed. Resultantly, the executing method about real time detection during scratching is determined, which acts as a foundation for the closed loop control of scratching depth.By application of the micro/nano plastic mechanics, the indenting and depth forming processes using the diamond tip of AFM cantilever on the sample's surfaces are analyzed. And then the forming rule of scratching depth corresponding to the scratching driving is investigated to set up the object model. And in terms of the automatic control theory and the optimized design of controller and control algorithm, the automatic and accurate closed-loop control for scratching depth is realized. Moreover, the variation rule of scratching depth is investigated through finite element simulations, in which the control scheme for scratching depth is determined. Finally, the accurate and closed loop control system for scratching depth is realized.The associated assistant control equipments are developed by using the computer and microprocessor techniques. The machining system integrated with AFM and 3D high precision stage, is established, which can perform the fabrication and measuring procedures and enables the scratching depth to be controlled automatically and accurately. Based on this setup, the fabrication of 3D microstructures with a design depth is carried out. Moreover, the 3D microstructures characterized with the continuous curved faces or other complicated faces all can be fabricated.