Ultralow voltage (1µV) electrical switching of SnS thin films driven by a vertical electric field.

In this paper, we show in a series of experiments on 10 nm thick SnS thin film-based back-gate transistors that in the absence of the gate voltage, the drain current versus drain voltage (ID-VD) dependence is characterized by a weak drain current and by an ambipolar transport mechanism. When we apply a gate voltage as low as 1µV, the current increases by several orders of magnitude and theID-VDdependence changes drastically, with the SnS behaving as ap-type semiconductor. This happens because the current flows from the source (S) to the drain (D) electrode through a discontinuous superficial region of the SnS film when no gate voltage is applied. On the contrary, when minute gate voltages are applied, the vertical electric field applied to the multilayer SnS induces a change in the flow path of the charge carriers, involving the inner and continuous SnS layer in the electrical conduction. Moreover, we show that high gate voltages can tune significantly the SnS bandgap.

Ultrathin tin sulfide field-effect transistors with subthreshold slope below 60 mV/decade.

In this paper, we present for the first time a field-effect-transistor (FET) having a 10 nm thick tin sulfide (SnS) channel fabricated at the wafer scale with high reproducibility. SnS-based FETs are in on-state for increasing positive back-gate voltages up to 6 V, whereas the off-state is attained for negative back-gate voltages not exceeding -6 V, the on/off ratio being in the range 102-103depending on FET dimensions. The SnS FETs show a subthreshold slope (SS) below 60 mV/decade thanks to the in-plane ferroelectricity of SnS and attaining a minimum value SS = 21 mV/decade. Moreover, the low SS values can be explained by the existence of a negative value of the capacitance of the SnS thin film up to 10 GHz (for any DC bias voltage between 1 and 5 V), with the minimum value being -12.87 pF at 0.1 GHz.

The microwave properties of tin sulfide thin films prepared by RF magnetron sputtering techniques.

In this paper we present the microwave properties of tin sulfide (SnS) thin films with the thickness of just 10 nm, grown by RF magnetron sputtering techniques on a 4 inch silicon dioxide/high-resistivity silicon wafer. In this respect, interdigitated capacitors in coplanar waveguide technology were fabricated directly on the SnS film to be used as both phase shifters and detectors, depending on the ferroelectric or semiconductor behaviour of the SnS material. The ferroelectricity of the semiconducting thin layer manifests itself in a strong dependence of the electrical permittivity on the applied DC bias voltage, which induces a phase shift of 30 degrees mm-1at 1 GHz and of 8 degrees mm-1at 10 GHz, whereas the transmission losses are less than 2 dB in the frequency range 2-20 GHz. We have also investigated the microwave detection properties of SnS, obtaining at 1 GHz a voltage responsivity of about 30 mV mW-1in the unbiased case and with an input power level of only 16µW.