Development Of Dynamic AFM Measurement System Based On New Type Tuning Fork Probe

With the development of micro-nanometer manufacturing technology, the relatedmicro-nanometer detection technology has been put higher demand, the demandreflects in the aspects of measuring range, measuring accuracy and the measuringvelocity. Atomic force microscope (AFM) is an important method formicro-nanometer detection, it can measure the topography of micro component andthe resolution can reach nanometer level. The dynamic AFM, which combines AFMhead with large range and high precision positioning stage and achieves millimeterlevel measurement range and nanometer level resolution, is the development focus inrecent years.In this dissertation, based on investigating the AFM research status anddevelopment trend, a dynamic AFM measurement system which combines theself-sensing tuning fork head with large range nanometer positioning stage (NMM)has been set up. The main work of the research includes the following aspects:1. The tuning fork probe working principle is explained by introducing the tuningfork probe structure characteristics. Two resonant frequencies of the tuning fork probeare found with the established mechanical model and the selection of tuning forkprobe’s working frequency is discussed. The influence of the internal parasiticcapacitance on the tuning fork probe is analyzed with the electrical propertiesobtaining from the electrical model. The principles of the dynamic AFM’s threeworking modes are introduced and the differences between them are discussed.2. A small AFM head based on the self-sensing tuning fork probe is developed. Asignal processing circuit of the tuning fork probe which can amplify the self-sensingsignal and compensate the parasitic capacitance is designed. A large range AFMsystem, with the combination of the self-sensing tuning fork head and the nanometerpositioning stage with long movement range, is developed. And the measurementresults of this system are traceable. A feedback signal controller with digital PIfeedback system which uses DSP as the core is developed. The measuring system canachieve a variety of measuring modes. Through the switch on the controller, themeasuring modes can be fast switched without changing the circuit connection.3. The relationship between excitation signal and the tuning fork probe current has been gotten through extracting the nanoampere-level weak signal of the tuningfork probe. The probe’s electromechanical coupling factor has been calibrated byusing micro Laser Doppler technology for measuring the mechanical amplitude oftuning fork probe. The effect of temperature and environmental vibration onparameters of the tuning fork probe, such as quality factor, resonance frequency, isdiscussed. The performance of feedback control module is tested. At last, for provingthe system’s feasibility, the AFM measuring system accomplishes the measurement ofstandard grid structure in the frequency modulation and the phase modulation modes.