Study On Piezoelectric Inchworm-type Probe-approaching Stepper

Scanning tunneling microscope (STM) is one of the advantageous instruments for nano technology. The probe approaching devices, which determined the structure and the performance of STM, are key components in it. However, the stepping motors, which are used for probe approaching in STM conventionally, are exothermic and unstable, especially for fine scanning. The drifts caused by the motor will influence the scanning image as additional noises or even make the scanner beyond the range of stable tracking.A piezoelectric inchworm-style stepper is designed for probe approaching in this paper. Flexible hinges and PZT stacks are used to constitute the stepper. The stepper achieves a theoretical range of 50mm and the deviation of each step is less than 6nm. The stepper performed steadily and reliably, and with a clamping mechanism it can not only be used for horizontal direction but also for vertical direction.The main research works are listed as follows:1. The various probe approaching steppers in STM are studied primitively. The features of each stepper on structure, work stability, assembly and other aspects are summarized a piezoelectric inchworm-type device is chosen as the best proposal.2. The structure of the stepper is designed, including the clamping mechanism and middle eight-bar linkage mechanism, ANSYS is utilized to analyze and optimize the structure of the mechanism.3. According to the work principle of the stepper, the control timing sequences is designed, and the whole hardware control circuits are designed in order to achieve the inchworm-style movements.4. The performance of the stepper in the horizontal direction and vertical direction are tested by the laser interferometer, including the single step of the stepper, the linearity of the middle eight-bar linkage mechanism and the speed of the stepper.5. The stepper is employed to achieve a probe approaching experiment. The detection circuit for the measurement of the tunneling current and a test system are designed to act in concert with the stepper.