The widespread adoption of metal oxide semiconductor field effect transistors (MOSFETs) has
prompted the development of advanced characterization methods of said devices. A specific quantity of
interest is how many atomic scale defects exist in a particular device. In MOSFETs, differing lattice
structures between the semiconductor and oxide leave some bonds unsatisfied at the interface between the
two materials. These unsatisfied bonds (or defects) have the ability to capture electrons and by extension
impact the electronic properties of devices, which have little tolerance for error. One method for
determining defect density is known as charge pumping (CP).
In CP a transistor is configured such that when a square wave voltage is applied to the gate, a
recombination current can be measured through the substrate. The measured current is proportional to the
defect density as well as the frequency of the square wave, and can be used to “count” the defects. The
technique has been used extensively in research and industry, and several advancements have allowed CP
to be used even in highly-scaled MOSFETs. Other efforts have been made to extract more information
from the response aside from just defect density.
This talk will discuss two advanced CP techniques. Frequency modulated CP (FMCP) can be used to
eliminate leakage currents which obscure the CP response. While CP current is proportional to frequency,
leakage current is not, so when the CP frequency is modulated and the signal is examined using a lock-in
amplifier, the CP current is amplified but the leakage is not. A second technique known as spin-dependent
CP (SDCP) incorporates electron spin resonance into the CP detection. The resulting response can be
interpreted to give chemical and physical information about the defects themselves. The potential
combination of FMCP and SDCP will also be discussed. Successful FM SDCP would be instrumental in
making further improvements in state-of-the-art integrated circuits, and could aid in the development of a
CP-based quantized current source.
