Scanning tunneling microscope (STM) is a versatile tool for imaging of conductive material surfaces, with atomic resolution. It can also be used as a tool for nanolithography, e.g. to produce atomically precise patterns on hydrogen-terminated silicon. A typical STM consists of a conductive probe with a nanometer-sharp tip attached to a three-degree-of-freedom (3DOF) piezotube, which can precisely position the tip several angstroms away from the sample surface. When an electrical potential is applied between the tip and the sample, current starts tunneling through the tip-sample gap. Amplitude of the tunneling current is exponentially proportional to the tip-sample separation and is thus highly sensitive to minute movements.
Despite its widespread use, scan speed and throughput of the conventional STM has remained limited over the last four decades. With a typical STM, it could take several minutes to acquire a single image. STM-based lithography is even a slower process. The low bandwidth of the STM’s closed-loop system, typically less than 1kHz, is a limiting factor in achieving higher scan speeds.
We are developing a novel 1-DOF nanopositioner featuring electrostatic actuators and an FIB tip for imaging, which provides an open-loop Z axis an order of magnitude higher than conventional STM scanners. The device is designed to be integrated into existing commercial STM piezopositioners, replacing STM tip and Z-positioning functionalities. It is microfabricated using double Silicon-on-Isolator (SOI) technology, and standard cleanroom instruments.