Carnegie Mellon University


Devices - cleanroom

Computer technology is facing a number of bottlenecks that block the increase of speed, energy efficiency, and cost per computation. The bottlenecks can originate form the intrinsic nature of the elementary building block of VLSI circuits, the CMOS transistor, or from the system architecture (for example a well known von Neumann bottleneck). The solutions range from novel devices such as non-volatile memory elements to novel architectures such as oscillatory neural networks.

Resistive switching devices for non-volatile ultra-dense memories
Currently we target two types of non-volatile switching (memory) devices: oxide Resistive Random Access Memories relying on the Valence Change Mechanism and phase change RAM based on Ge2Sb2Te5 and related chalcogenides. We focus on development of new functional materials, identification of the mechanisms involved in resistive switching, advanced metrology, and simulation.Devices - switching IVDevices - 3d crosspoint

Oxide-based threshold switches
Threshold switch is similar in function to a memory switch. It also has two different states of resistance and switches from high to low resistance if the voltage exceeds the threshold but the switch is volatile and "forgets" its state when the bias is removed. Threshold switches are used as two terminal devices with applications as selection devices in memory arrays and oscillators.

3D XPoint memory announced by Intel and Micron in July 2015 includes resistive switching devices and threshold switches.

Devices - schematics

The simplest of threshold switching devices consists of two metallic electrodes with a layer of vanadium dioxide in between (lateral device is shown in the figure). VO2 is one of the strongly correlated electrons oxides which exhibit a metal-insulator transition. At temperatures below 61 oC, VO2 is a leaky insulator and transforms to a metal above. In nanoscale devices, the leakage current at 1-2 V is sufficiently high to generate enough heat and switch the VO2 to a metal effectively shorting the electrodes. What is truly interesting is the possibility of inducing the MIT by application of electric field rather than heat.

Devices - 240k-18v-steady-2Devices - 240k-18v-steady-1

Electro-thermal finite element simulation of the current and heat distribution in VO2-based threshold switch.

Funding:                                                 Collaborations:

Devices - StarNetDevices - DarpaDevices - SRC                                  Devices - CMU-ECEDevices - IntelDevices - International Medical Equipment CollaborativeDevices - CornellDevices - Nortre Dame

Recent Publications:
  1. "Thermometry of Filamentary RRAM Devices", E. Yalon, A. A. Sharma, M. Skowronski, J. A. Bain, D. Ritter, and I. V. Karpov, " IEEE Trans. Electron Dev. 62, 2972 (2015)

  2. "High-Frequency TaOx-Based Compact Oscillators", A. A. Sharma, Y. Li, M. Skowronski, J. A. Bain, and J. A. Weldon, IEEE Trans. Electron Dev. 62, 3857 (2015)

  3. "Dynamics of electroforming in binary metal oxide-based resistive switching memory", A. A. Sharma, I. V. Karpov, R. Kotlyar, J. Kwon, M. Skowronski, and J. A. Bain, J. Appl. Phys.  118, 114903 (2015)

  4. "Electronic instabilities leading to electroformation of binary metal oxide-based resistive switches", A. A. Sharma, M. Noman, M. Adbelmoula, M. Skowronski, and J. A. Bain, Adv. Funct. Mater. 24, 5522 (2014)

  5. "Mechanism of localized electrical conduction at the onset of electroforming in TiO2 based resistive switching devices", M. Noman, A. A. Sharma, Y. M. Lu, R. Kamaladasa, M. Skowronski, P. A. Salvador, and J. A. Bain, Appl.
    Phys. Lett. 104, 113510 (2014)

  6. "Impact of Joule heating on the microstructure of nanoscale TiO2 switching devices", Y. M. Lu, M. Noman, Y. N. Picard, J. A. Bain, P. A. Salvador, and M. Skowronski, J. Appl. Phys. 113, 163703 (2013)

  7. "Transient characterization of the electroforming process in TiO2 based resistive switching devices", M. Noman, A. A. Sharma, Y. M. Lu, M. Skowronski, P. A. Salvador, and J. A. Bain, Appl. Phys. Lett. 102, 023507 (2013)

  8. "Elimination of high transient currents and electrode damage during electroformation of TiO2-based resistive switching devices", Y. M. Lu, M. Noman, W. Chen, P. A. Salvador, J. A. Bain, and M. Skowronski, J. Phys. D Appl. Phys. 45, 395101 (2012)

  9. "Mobility of oxygen vacancy in SrTiO3 and its implications for oxygen-migration-based resistance switching", W. Jiang, M. Noman, Y. M. Lu, J. A. Bain, P. A. Salvador, and M. Skowronski, J. Appl. Phys. 110, 034509 (2011)

  10. “Computational investigations into the operating window of memristive devices based on homogeneous ionic motion” M. Noman, W. K. Jiang, P. A. Salvador, M. Skowronski, and J. A. Bain, Appl. Phys. A: Mat. Sci. and Proc. 102, 877 (2011)

  11. “Electrical characterization of 4H-SiC avalanche photodiodes containing threading edge and screw dislocations” R. A. Berechman, M. Skowronski, S. Soloviev, and J. Appl. Phys. 107, 114504 (2010)