Non-volatile memristors are promising for future hardware-based neurocomputation application because they are capable of emulating biological synaptic functions. Various material strategies have been studied to pursue better device performance, such as lower energy cost, better biological plausibility, etc. In this work, we show a novel design for non-volatile memristor based on CoO/Nb:SrTiO3 heterojunction. We found the memristor intrinsically exhibited resistivity switching behaviors, which can be ascribed to the migration of oxygen vacancies and charge trapping and detrapping at the heterojunction interface. The carrier trapping/detrapping level can be finely adjusted by regulating voltage amplitudes. Gradual conductance modulation can therefore be realized by using proper voltage pulse stimulations. And the spike-timing-dependent plasticity, an important Hebbian learning rule has been implemented in the device. Our results indicate the possibility of achieving artificial synapses with CoO/Nb:SrTiO3 heterojunction. Compared with filamentary-type of synaptic device, our device has potential to reduce energy consumption, realize large scale neuromorphic system, and work more reliably, since no structural distortion occurs.
Figure 1 Conductance characterization of the synaptic device
Electrical characteristics of CoO/Nb:SrTiO3 heterojunctions measured by a Keithley 2400. Current was applied to the device and voltages were measured. The conductance of the device can be calculated.
Open_Science_ConductanceCharacterization.xlsx
Inset of Figure 1(d) The time dependence of the current at the LRS and the fitting curve
Electrical characteristics of CoO/Nb:SrTiO3 heterojunctions measured by a Keithley 2400. The time dependence of the current at the LRS was fitted with a bi-exponential relaxation equation.
Open_Science_TimeDependenceOfCurrent.xlsx
Figure 2(a) Resistance shift in CoO/NSTO device
The amplitudes of the stimuli pulses were recorded. The resistance here was calculated by dividing the measured_voltage by measured_current.
Open_Science_ResistanceThreshold.xlsx
Figure 2(b) Dependence of the device resistance on the pulse amplitude and pulse number
The device was stimulated by square with varying amplitudes. Pulses were numbered by 1,2,3,....Resistance was measured after each pulse. The resistance recorded here was calculated by dividing the measured_voltage by measured_current.
Open_Science_LongTermPotentiation.xlsx
Figure 3 Resistance switching cycles and the consecutive positive or negative stimuli pulses.
The device was stimulated by step pulses. Pulses were numbered by 1,2,3,.... Resistance was measured after each pulse. The resistance recorded here was calculated by dividing the measured_voltage by measured_current.
Open_Science_ResistanceModulation.xlsx
Figure4 The STDP response of the electronic synapse
The stimuli spikes were generated by programming a data acquisition card (NI PCI6259) and recorded. The device was stimulated by spike pairs. The resulting timing-dependent resistance modulation was studied by recording the ∆t(spikTimingDifference) and the device conductance change (SynapticWeightChange(%)).
Open_Science_STDP.xlsx
