This work investigates scanning laser annealing used for ultra-shallow junction (USJ) activation. We investigate the laser system via simulation to determine the peak temperature achieved in the active area during processing. We employed the Sentaurus TCAD software by Synopsys to perform a 2D simulation of a laser scans across the active area of the device, solving the heat equation in both time and space. An absorber layer is deposited on the wafer surface to enhance the absorption of incident energy and reduce SOI reflectivity. An effective absorption coefficient of α=8000cm-1 was calculated for the absorber layer, calibrated with the experimental laser intensity. This absorption coefficient correctly predicts the silicon temperature as a function of power with any arbitrarily defined scan speed. To investigate the role of dopant activation, an SOI wafer was implanted with arsenic 25 keV, dose 3e15 /1.5e15 cm-2 and laser annealed in areas of target temperatures ranging from 850-1300°C. The sheet resistance was measured using 4-point probe showing sheet resistance improvement with increasing laser temperature. The extracted temperature cycle from the 2D heat simulation was used as an equivalent millisecond RTA in a full 3D process simulation to study dopant distribution and activation using Sentaurus Process Kinetic Monte Carlo (KMC), considering the effect of dopants, dopant clusters, and point defects. The results of this simulation demonstrate deactivation of arsenic above 1050°C, which is inconsistent with Hall measurements that suggest increasing laser temperature will increase mobility and activation. The results are analyzed versus the expected trends and suggest future improvements needed to the KMC model or the laser temperature profiles in order to describe activation kinetics in millisecond anneals within SOI.

The influence of the red and green LED light exposure on the memory function of the nanocrystalline MoOx embedded ZrHfO high-k gate dielectric has been investigated. Since the performance of the device is mainly dependent on the hole trapping and detrapping mechanisms, the light exposure affects the hole generation, transfer, and storage to and in the dielectric structure. Both the charge storage capacity and the leakage current were increased from the light exposure. The Coulomb blockade phenomenon in the leakage current density vs. gate voltage curve disappears under the light exposure condition. The light exposure effect is potentially important for practical application of the device.

Forming voltage (VForm) and initial resistance of NiO-based resistive switching (RS) cells with various NiO films were investigated. Deposited NiO films were 〈111〉-oriented and the lattice constant was larger than that of bulk. It was revealed from XRD analyses that there were residual compressive stresses in NiO films. The magnitude of the residual stress was different among NiO films depending on their deposition conditions, and VForm monotonically increases with the increase in the magnitude of the residual stress. The relationship between VForm and the residual stress may be ascribed to the changes in the density of oxygen vacancies in NiO films. NiO films were also post annealed in Ar at 450°C. RS cells with annealed NiO films having small oxygen composition exhibited forming-free behavior, indicating the generation of conductive filaments by the annealing. The region whose lattice constant is smaller than that of bulk appeared after annealing only in such NiO films, suggesting that the small lattice-constant region may be linked to the generation of the filaments.

MOS capacitor composed of nc-CdSe embedded ZrHfO high-k gate dielectric stack was fabricated and characterized for nonvolatile memory functions. Detailed material and electrical properties have been investigated. With a large charge trapping capability, this kind of device can trap electrons or holes depending on the polarity and magnitude of the applied gate voltage. For the same stress time, the device trapped more holes than electrons under the same magnitude of gate voltage but different polarity. The negative differential resistance peak was observed at the room temperature due to the Coulomb blockade effect. The charge trapping mechanism was delineated with the constant voltage stress test. After 10 years of storage, about 56% of trapped charges still remain in the device.

The narrow gap Mott insulators AM4Q8 (A = Ga, Ge; M= V, Nb, Ta; Q = S, Se) exhibit very interesting electronic properties when pressurized or chemically doped. We have recently discovered that the application of short electrical pulses on these compounds induces a new phenomenon of volatile or nonvolatile resistive switching. The volatile transition appears above threshold electric fields of a few kV/cm, while for higher electric fields, the resistive switching becomes non-volatile. The application of successive very short electric pulses enables to go back and forth between the high and low resistance states. All our results indicate that the resistive switching discovered in the GaM4Q8 compounds does not match with any previously described mechanisms. Conversely, our recent work shows that the volatile resistive switching is related to a purely electronic mechanism which suggests that the AM4Q8 compounds belong to a new class of Mott-memories for which Joule heating, thermochemical or electrochemical effects are not involved. Finally, it is possible to deposit a thin layer of GaV4S8 and to retrieve the reversible resistive switching on a metal-insulator-metal (MIM) device which proves the potential of this new class of Mott-memories for applications.

A phenomenological model has been proposed for the radial growth of the copper or silver nanobridge in the conductive bridge random access memory devices. In this model, the growth rate of the bridge is proportional to the local ion flux based on the hopping mechanism. Due to the differences of the local electric field, the growth rate is different along a conical shape nanobridge. The model accounts for the growth rate difference by introducing a geometrical form factor. Based on the model, the top and bottom radii are predicted for truncated conical copper nanobridge. The model is validated with data obtained on Cu/TaOx/Pt resistive devices.

Nonvolatile unipolar resistive switching properties of the amorphous LaGdO3 thin films deposited by pulsed laser deposition have been studied. Reliable and repeatable switching of the resistance of LaGdO3 film was obtained between low and high resistance states with nearly constant resistance ratio ∼ 106 and non-overlapping switching voltages in the range of ∼0.6-0.75 V and 2.5-4 V respectively. The switching between low and high resistance states was attributed to the formation and rupture of conductive filaments using temperature dependent resistance measurements. The current conduction mechanisms of the LaGdO3 film in low and high resistance states were found to follow the Ohmic behavior and Poole-Frenkel emission respectively. The resistance of low and high resistance states of the film remained nearly constant for up to ∼ 104 seconds indicating good retention. The observed resistive switching characteristics of LaGdO3 thin films are promising for futuristic nonvolatile memories.

We present results of first-principles non-equilibrium Green’s function calculations for current-voltage (IV) characteristics of the electrode/HfO2/electrode model systems. In order to investigate the effect of the electrode materials on the IV characteristics, we considered two transition metals for electrode, Ta and W, which are both body-centered-cubic elemental metals but have different valence numbers. We simulated the ON state by placing oxygen vacancies in the HfO2 layer while the OFF state was modeled with HfO2 without oxygen vacancies. At the OFF state, no electric current flowed for -1 V up to +1 V, as expected. At the ON state, however, we found that the absolute current for the Ta electrode was twice as large as that for the W electrode. The analysis of the IV characteristics shows that the electronic coupling between Ta and HfO2 is substantially stronger than that between W and HfO2. Our study demonstrates the importance of the matching between electrode and insulator materials to achieve a high ON- to OFF-current ratio in ReRAMs at a low bias.

Clarification of memory characteristics of tiny cell is important for practical use of resistive random access memory (ReRAM). However, limitation of semiconductor micro-fabrication technology hinders to obtain memory characteristics in tiny cell with an area comparable to the size of filaments. In this paper, we established a method to prepare a very small memory cell by fabricating ReRAM structure on the tip of a cantilever of atomic force microscope (AFM). We also established a method to avoid the overshoot of set current. As a result, reset current was successfully reduced enough to suppress serious damage to the cantilever. The effective cell size was estimated to be less than 10 nm in diameter due to electric field concentration at the tip of the cantilever, which was confirmed by an electric field simulator based on finite element method. We performed a unique experiment to verify the presence of oxygen pool in an anode, by utilizing removable bottom electrode structure. The result was not consistent with resistive switching models that require the anode to play a role as an oxygen reservoir.

To better understand the mechanisms of creation and rupture of conductive filaments in resistive switching devices such as Cu/TaOx/Pt, with Cu and Pt being the active and inert electrodes, respectively, a device with limited supply of active metal electrode has been manufactured and electrically characterized. The limited supply of active metal has been realized by depositing a thin (delta) Cu layer (δ-Cu), 6 nm and 12 nm thick, on TaOx, resulting in a Pt/δ-Cu/TaOx/Pt device structure. The limited active metal supply i) has a direct impact on the onresistance (Ron) of the Cu bridge, and leads, after several conventional set-reset cycles, to ii) pulsating behavior, when device turns on and off repeatedly, to iii) symmetric switching behavior with respect to applied voltage polarity, when the device can be set and reset both at positive and negative bias, and to iv) volatile switching behavior.

We investigated quantization behavior in conductance of an Ag/Ta2O5/Pt gapless-type atomic switch. Stepwise increases and decreases in the conductance were observed when small positive and negative bias voltages were applied to the Ag electrode, respectively, where each step corresponds to the conductance of a single atomic point contact. The conductance level could also be controlled by applying voltage pulses with varied amplitudes. Furthermore, when the interval time of consecutive input pulses was turned, we also observed long-term potentiation behavior similar to that of biological synapses. These results indicate that the oxide-based, gapless-type atomic switch has potential for use as a building block of neural computing systems.