Preparation And Performance Study Of A Strain Force Sensor For Double-ended Supported Elastic Beam-membrane Structure Film

Measuring cutting force is an effective method for processing status monitoring in intelligent manufacturing.It can provide data support for cutting fault prediction,tool life research and cutting parameter optimization.Film strain force sensor is widely used because of its high accuracy and reliability.In this paper,a sensitive layer structure with double-ended supported beam-membrane structure is proposed for micro-strain measurement based on traditional flat-membrane structure thin-film strain sensor by combining theoretical analysis with experimental analysis.The geometric parameters of the beam-membrane structure of the sensitive layer are designed by the principle of linear output design of the sensor.Two preparation processes for removing the sacrificial layer are designed.The layout,size and size of the resistance grid of the sensitive layer are also designed.Using Stoney classical film stress theory and film interface toughness theory,the influence of mismatch strain on the performance of double-layer film system is analyzed.Mathematical models of mismatch strain and film thickness of transition layer,insulation layer are established.In order to make the membrane strain sensor suitable for higher impact rate strain processing conditions,and to provide the basis for subsequent preparation of the membrane structure sensitive layer film.Titanium nitride transition layer and silicon nitride insulation layer were prepared on 304 stainless steel substrates by DC reactive magnetron sputtering and plasma enhanced chemical vapor deposition(PECVD),titanium nitride film/silicon nitride constitutes a composite insulating layer film with both hardness and resistance to plastic deformation.The preparation process of Ti N was described in detail.The influence of negativebias and nitrogen flow on the surface morphology and microstructure of Ti N film was investigated by atomic force microscopy(AFM).The relationship between Ti N(111)and Ti N(200)peak orientation,peak intensity transformation,texture coefficient,lattice spacing and nitrogen flow was analyzed by X-ray diffraction(XRD).The influence of peak orientation of Ti N(200)on the smoothness of Ti N film was analyzed by atomic force microscopy(AFM).Afterwards,the effects of different film thickness on the hardness of the film system and the plastic deformation resistance of the film were studied by nanoindentation experiments.Linear fitting between the toughness and nano-hardness of the film revealed that the nano-composite film with higher hardness usually has higher H~3/E~2ratio.The previous Stoney theory analysis was verified by experiments.According to the preparation process designed in Chapter 2,a composite Ti N/Si₃N₄layer with a thickness of 800 and 100 nm was selected as the insulating layer to deposit the sacrificial layer and the sensitive layer of nickel-chromium(Ni₈₀Cr₂₀)to prepare the membrane strain sensor with beam-membrane structure.The effects of argon flow rates on the deposition rate and surface morphology of Al and Sn sacrificial layers were investigated.The uniformity of element distribution in the sacrificial layers after first photolithography and ion beam etching was qualitatively analyzed by scanning electron microscopy(SEM)and scanning electron microscopy(SEM-EDS)combined with X-ray photoelectron.The element distribution of the samples after the second lithography development and the structure of the samples after the removal of the sacrificial layer were also characterized by using the scanning mode of SEM-EDS and the scanning mode of optical profiler.The optimum wet etching process was determined by observing the surface morphology of the wet etched nickel-chromium film by using the scanning electron microscope.Finally,the finished product of the film strain sensor is obtained after the third photolithography development.