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Resistive Switching Devices

Fig. 1
Fig. 1: Non-volatile capacitance hysteresis measured in a capacitor structure with an Al2O3/ Nb2O5 double layer sandwiched in between two TiN electrodes.

The central aim of our research on Resistive Switching Devices is the development of device structures, capable of changing their electrical resistance or capacitance by applying external voltages. The resistive memory device – the so called RRAM – is one of the potential candidates for the realization of embedded memories or storage class memory, since it is characterized by very fast access times, non-volatility, and low power consumption. A further interest is the application of such reconfigurable devices in neuromorphic nano-circuits, exhibiting the united functionality of logic and memory in one device. Our activities cover the deposition and modification of dielectric thin films and electrode layers, the physical and electrical characterization as well as the modeling of the switching properties.

Our research focuses on niobium oxide based resistive switching devices. By variation of the fabrication process, electrode materials and thin film composition a large variety of different switching characteristics could be obtained. Besides the pure resistance switching we found a capacitance switching effect in a bilayer device of TiN/ Al2O3/ Nb2O5/ TiN stack.

Fig. 2
Fig. 2: Realization of an oscillator circuit using bonded NbOx-based threshold switching devices.

 

 

Fig. 1 depicts the measured capacitance of such a device when sweeping the bias voltage from -4 V to 4 V and back. A non-volatile capacitance hysteresis can be observed. That effect opens the opportunity to develop novel circuits such as tunable oscillators.

Another focus of our research is the development of active electronic circuits based on locally active devices. The negative differential resistance branch in the I-V characteristic of the device results in local activity, which is the ability of the device to amplify infinitesimal fluctuations in energy.  

Fig. 3
Fig. 3:  Layout of a multi-functional test chip for statistical investigation of resistive memory elements.

 

This particular characteristic offers the possibility to create active electronic circuits which possibly could replace conventional transistor based devices in some applications. In order to enable the realization and investigation of basic circuits we further developed our manufacturing process to package the nano-devices. Fig. 2 shows a photograph of a package including 4 locally active memristor devices connected in a circuit.

The control of parameter variability of nano-devices plays an important role for their adoption in large integrated circuits. Therefore a multiplexed array structure was developed that allows the direct access to 64k two terminal devices in a single test structure (layout depicted in Fig. 3) for statistical characterization. Different material combinations can be easily integrated.

 

Contact: Dr. Stefan Slesazeck

 

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