Step edge cut off — A new fabrication process for metal-based single electron devices

Abstract

Proper operation of single electron devices is restricted to tempertures where the charging energy of one single electron is well above its thermal energy. Liquid helium operation, for example, requires device capacitances below 55 aF. A single electron transistor (SET) consists of three capacitors, a conventional gate capacitor and two tunneling capacitors forming source and drain. Therefore the fabrication of 20 aF tunneling capacitances is the prerequisite for a 4.2 K SET. Conventional fabrication processes require sub-20 nm electron beam lithography to achieve such small tunneling capacitances. The new step edge cut off process presented here has drastically relaxed technological requirements. Tunneling capacitances of 8 aF were realized in metal based structures, using a 100 nm design. Liquid helium operation was demonstrated and traces of single electron effects were observable up to 20 K. A further increase in operating temperature can be achieved with both smaller structure sizes and low dielectric materials.