TESTING

To verify the accuracy of the diode equivalent model, a prototype MoS2-based frequency multiplier is fabricated and tested by connecting it to an RF signal source and spectrum analyzer. The RF signal source provides a fixed input frequency of 1 GHz at 20 dBm (see Figure 5).

Figure 6

Figure 6 MoS2 frequency doubler output spectrum (V0 = 0 V).

Figure 7

Figure 7 MoS2 frequency doubler output spectrum (V0 = 21 V).

After measuring the output without bias voltage, input DC bias is gradually increased to 30 V in 0.5 V steps. As a function of voltage, the second and third harmonic is observed on the spectrum analyzer. Figure 6 shows the spectrum at 0 V where the second harmonic output power is below -60 dBm. Figure 7 shows the spectrum at 21 V (determined to be optimum for this MoS2 sample). Optimum bias is dependent upon the MoS2 film thickness and crystal structure. At 21 V bias, the output power at the second harmonic is -27 dBm. The trend with bias voltage is shown in Figure 8.

Figure 8

Figure 8 Output power at the second harmonic as a function of bias voltage at a fixed input power of 20 dBm.

Figure 9

Figure 9 Output power at the second harmonic as a function of input power at a fixed bias of 21 V.

With a fixed bias voltage of 21 V, Figure 9 shows output power of the second harmonic as a function of input power. The output power gradually increases when the frequency and bias voltage are fixed.

CONCLUSION

A voltage-controllable microwave frequency doubler is based on a 2D MoS2 film. MoS2 film possesses strong nonlinear characteristics, and its nonlinear efficiency is further improved with applied DC bias. In this work, a frequency doubler is developed leveraging these characteristics. With an input power of 20 dBm at 1 GHz, the output power of the second harmonic is below -60 dBm without bias voltage applied. With 21 V bias applied, the output power of the second harmonic is -27 dBm, an improvement of 33 dB. Simulation using a theoretical model equating the MoS2 film to a reverse parallel diode pair agrees well with measurements.

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