Noise Mitigation for Ballistic Electron Emission Microscopy Instrumentation

The evolution of nanoelectronics is driving the use of new materials and electron transport phenomena, generating a growing interest in understanding how interfaces and buried structures influence nanoelectronics' performance. Ballistic electron emission microscopy (BEEM) is a scanning tunneling microscope (STM) technique for mapping Schottky barriers with nanometer lateral resolution and meV energy resolution which can probe nanoelectronic interfaces. BEEM data acquisition is rate limited by signal to noise ratios to approximately an order of magnitude slower than STM which limits its applications in nanoelectronics metrology. We will describe the optimization of signal to noise ratios in a commercial STM modified for BEEM capabilities. By minimizing the coaxial cable length we show that noise is reduced from 99 fA/√Hz down to 63 fA/√Hz at 1.1 kHz bandwidth. We expect that this noise can be lowered, approaching a limit set by commercial transimpedance amplifiers at 24 fA/√Hz which would result in a significantly faster measurement.