Micromechanical electrometry of single-electron transistor island charge

Abstract

We consider the possibility of using a micromechanical gate electrode located just above the island of a single-electron transistor to measure directly the fluctuating island charge due to tunnelling electrons.

Room temperature electrometry with SUB-10 electron charge resolution

“…When the responsivities of S1 and S2 are compared, taking into account the ratios of sense capacitances in each case, these agree well with equation (6). For a large C P , much greater than the sense capacitance (C S ), the responsivity scales with C S .…”

“…A comparison between the measured and predicted values for the responsivity, as summarized in table 2, shows that the two are in reasonably good agreement. Having shown that equation (6) and figure 7 agree very well with experimental data, these can then now be used as reliable reference for designing future electrometers of improved responsivities and charge resolution.…”

“…Conversely, the parasitic capacitance between the sense electrodes and ground is larger if the underlying substrate is not removed as in the case of [14]. Equation (6) shows that the responsivity increases with decreasing parasitic capacitance at input node which, as will be illustrated later in section 5, is a key factor in determining the electrometer resolution. It has been estimated that in the case of the structure described here, the presence of an underlying substrate would have contributed a minimum additional parasitic of 2 pF between the sense node and ground.…”

“…With a measured input referred voltage noise floor of 29 nV/ √ Hz at 6.4 kHz, this yields an equivalent charge noise floor of 6 e/ √ Hz. The parasitic at the input was too small to be measured, but equation (6) gives an estimate of approximately 2 pF.…”

“…In addition, electrometry has also been used in mass spectrometry for chemical and biological analyses [4]. At present, cryogenically cooled (few mK) singleelectron transistors (SETs) [5] are seen as the most sensitive of electrometers [6], capable of charge resolutions better than 10 −5 e/ √ Hz. Other solid-state solutions to high-resolution electrometry have included MOSFETs which are able to detect single electrons at a higher temperature of 8 K [7].…”