What is force feedback, and why is it important?
When contacting a surface, the tip of the probe is deflected a few nanometers and this probe deflection is measured with an optical beam. As the probe tip scans over the chip’s surface features, a force-feedback loop adjusts the height of the piezo actuator to compensate for the height of the feature. The probe tip is automatically lifted by the feedback loop to maintain a constant deflection and therefore a constant force between the tip and the surface. In this way, the deflection of the probe during imaging is be kept quite small (a few nanometers). Wth force feedback,the probe tip can have a high spring constant and still not apply large forces to the sample while imaging Without force feedback, the contact force changes as the probe tip deflects while scanning over features. Therefore, to avoid damage the tip must be extremely soft. Why not just use a soft tip? In order to be able to conduct electrical tests, the tip must also be able to generate considerable force to break though
