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^{1,a)}, A. Forchel

^{1}, I. Neri

^{2}, L. Gammaitoni

^{2}and L. Worschech

^{1}

### Abstract

The authors have fabricated branched resonant tunneling diodes (RTDs). Using two branches as inputs, universal logic-gate operation was investigated as a function of noise added to the input signal. The difference in the output voltage, used as a measure for logic operation, shows a peak in the noise power characteristic associated with logic stochastic resonance. The split RTD allows morphing between universal logic-gates solely controlled by the noise level with power differences in the nanowatt range.

The authors gratefully acknowledge financial support from the European Union [FPVI, STREP Contract No. 034236 SUBTLE, and FPVII (2007–2013) under Grant Agreement No. 256959 NANOPOWER] as well as the state of Bavaria. Expert technical assistance by M. Emmerling is acknowledged.

### Key Topics

- Random noise
- 7.0
- Stochastic processes
- 7.0
- Resonant tunneling diodes
- 5.0
- 1/f noise
- 4.0
- Machinery noise
- 4.0

## Figures

(Left) Layer sequence of the submicron-sized RTD. The double barrier consists of undoped 15 nm thick GaAs buffer layers, 3 nm thick barriers, and a 4 nm GaAs quantum well. (Right) Electron microscopy pictures of a branched RTD with a diameter together with the electronic circuit diagram. The dc working point voltage sets the working point of the RTD in the bistable regime. Additionally a time periodic signal with amplitude as well as an external noise source with standard deviation is applied. On each branch the logic inputs with switching voltages and are applied, and the voltage drop either at or is serving as output.

(Left) Layer sequence of the submicron-sized RTD. The double barrier consists of undoped 15 nm thick GaAs buffer layers, 3 nm thick barriers, and a 4 nm GaAs quantum well. (Right) Electron microscopy pictures of a branched RTD with a diameter together with the electronic circuit diagram. The dc working point voltage sets the working point of the RTD in the bistable regime. Additionally a time periodic signal with amplitude as well as an external noise source with standard deviation is applied. On each branch the logic inputs with switching voltages and are applied, and the voltage drop either at or is serving as output.

(a) Current-voltage characteristic of the branched RTD. At the working point a sine-wave periodic signal is applied, so that the bistable system is operated close to the threshold value . (b) Time series of the RTD output current I for the intrinsic noise level operated close to the threshold. Noise-induced neuronlike signal spikes are generated.

(a) Current-voltage characteristic of the branched RTD. At the working point a sine-wave periodic signal is applied, so that the bistable system is operated close to the threshold value . (b) Time series of the RTD output current I for the intrinsic noise level operated close to the threshold. Noise-induced neuronlike signal spikes are generated.

(a) Experimentally determined as a function of the noise power for logic inputs , 1, and 2 with switching voltages (0 mV) and (2 mV). The logical output is 1 for values exceeding the threshold voltage of 110 mV, and 0 below. is below the threshold for smaller than 0.7 nW and above for greater than 2 nW. No logic-gate operation can be depicted. Contrary, between and 1.2 nW the logical output is 1 only for both logical inputs 0. This fulfills the truth table of a logic NOR gate. Instead, for noise intensity above 1.2 nW only for both logical inputs 1 the logical output is 0. This can be recognized as a NAND gate. (b) Theoretical simulations with the experimentally obtained parameters agree with the experimental data.

(a) Experimentally determined as a function of the noise power for logic inputs , 1, and 2 with switching voltages (0 mV) and (2 mV). The logical output is 1 for values exceeding the threshold voltage of 110 mV, and 0 below. is below the threshold for smaller than 0.7 nW and above for greater than 2 nW. No logic-gate operation can be depicted. Contrary, between and 1.2 nW the logical output is 1 only for both logical inputs 0. This fulfills the truth table of a logic NOR gate. Instead, for noise intensity above 1.2 nW only for both logical inputs 1 the logical output is 0. This can be recognized as a NAND gate. (b) Theoretical simulations with the experimentally obtained parameters agree with the experimental data.

Mean value difference for the NOR and NAND gates as a function of the noise power for the experimental data in (a) and for the theoretically obtained data in (b). The mean value difference is defined as for the logic NOR gate and for the logic NAND gate. Two logic stochastic resonance maxima can be depicted. At the maximum corresponds to the logic NOR and at to the logic NAND gate.

Mean value difference for the NOR and NAND gates as a function of the noise power for the experimental data in (a) and for the theoretically obtained data in (b). The mean value difference is defined as for the logic NOR gate and for the logic NAND gate. Two logic stochastic resonance maxima can be depicted. At the maximum corresponds to the logic NOR and at to the logic NAND gate.

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