Capacitance Spectroscopy for MOS Systems

Producción CientíficaCapacitance studies of metal–oxide–semiconductor (MOS) capacitors have been used since the early 60s of the past century to investigates the interface surface states, oxide charge and electron and ion phenomena in these structures. This chapter provides detailed information about the theoretical basis, and examples of application of capacitance spectroscopy techniques in a variety of MOS systems

Control of the set and reset voltage polarity in anti-series and anti-parallel resistive switching structures

Producción CientíficaIn the attempt to control the polarity of the set and reset voltages in bipolar resistive switching capacitors, we have studied the switching properties of structures consisting of either two anti-series or two anti-parallel metal-insulator-metal capacitors. The capacitors were based on hafnium oxide, and W and TiN/Ti were used as bottom and top electrodes respectively. MIM capacitors showed bipolar resistive switching behavior, with very good repetitiveness and endurance properties. Both anti-series and anti-parallel structures showed again bipolar resistive switching behavior, being the polarity of the set and reset voltages controllable by applying higher biases. In the case of anti-series configuration, there is a stretch-out in the current-voltage characteristic because the bias is applied across two different devices. Changing the polarity is equivalent to the process of write and erase of complementary resistive switching devices in crossbar arrays. In the case of anti-parallel configuration, the resistance window between both resistivity states is reduced. The control of the switching polarity has also been observed when applying a small ac signal, and measuring the conductance of the structures.Ministerio de Economía, Industria y Competitividad - FEDER (project TEC2017-84321-C4-2-R

2020 IEEE Latin America Electron Devices Conference (LAEDC)

Producción CientíficaArtificial synaptic devices used in neuromorphic systems need a high number of reachable conductance levels. Resistive switching devices are promising candidates to implement these devices due to their reachable conductance levels. In this work, we have used TiN/Ti/HfO 2 /W capacitors to study the control of the intermediate conductance states using current pulses instead of the usual voltage pulses. Unlike the use of voltage pulses, in this case we can control the HRS to LRS transition (potentiation characteristic). The characteristic is clearly linear when applying current pulses with linearly increasing amplitudes. The potentiation characteristic is not affected by the pulse length, even for lengths lower than 1 μs. In terms of peripheral circuitry, it is desirable to use pulses with identical amplitudes, but in this case no accumulative behavior is observed, and one current pulse is enough to carry the device to the final conductance state achieved for the amplitude used. Finally, it is not possible to control the HRS to LRS transition (depression characteristic) using current pulses due to the abrupt reset transition. However, this transition can be well controlled using voltage pulses.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (grant TEC2017-84321- C4-2-R

Controlling the intermediate conductance states in RRAM devices for synaptic applications

Producción CientíficaRRAM devices are promising candidates to implement artificial synaptic devices for their use in neuromorphic systems, due to their high number or reachable conductance levels. The capacitors used in this work (TiN/Ti/ HfO2/W) show resistive switching behavior and reachable intermediate conductance states. We can control the conductance states by applying voltage pulses to the top electrode. Different approaches to control the synaptic weight have been studied: applying pulses with different voltage amplitudes changes the synaptic weight variation in an exponential way, and applying pulses with different lengths changes the synaptic weight in a linear way. We can control the conductance values when applying depression pulses, but the potentiation characteristic is not linear, as for other synaptic devices, as PRAMs. Applying other voltage signals to the structure, as voltage ramps, can improve the potentiation characteristic.Ministerio de Economía, Ciencia y Competitividad - Fondo Europeo de Desarrollo Regional (project TEC2017-84321-C4-2-R

Current pulses to control the conductance in RRAM devices

Producción CientíficaDue to the high number of reachable conductance levels in resistive switching devices, they are good candidates to implement artificial synaptic devices. In this work, we have studied the control of the intermediate conductance levels in HfO2-based MIM capacitors using current pulses. The set transition can be controlled in a linear way using this kind of signal. The potentiation characteristic is not affected by the pulse length due to the filament formation takes place in very short times. This behavior does not allow using identical pulses to obtain the potentiation characteristic. The transient response of the devices when applying current pulses showed the filament formation is characterized by a peak in the voltage transient signal. No depression characteristic can be obtained using current signals due to the abrupt reset transition. However, the depression characteristic can be obtained using voltage pulses, so combining both signals should allow control the synaptic weight in an appropriate way

Memory maps : Reading RRAM devices without power consumption

Producción CientíficaA comparative study of MIM-RRAM structures with different insulator materials is presented. Admittance memory mapping was carried out at 0 V dc bias, revealing two clearly separated states, both in terms of conductance and susceptance. The memory in the ON state can be modeled by means of a two parameter (resistance and inductance) equivalent circuit. The parameter extraction provides memory maps for the resistance and the inductance as well. The transition shapes between the ON and OFF state are different for each structure due to specific physical mechanisms.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (grant TEC2014-52152-C3-3-R)Fondo Europeo de Desarrollo Regional (project TK134)Estonian Research Agency (grants IUT2-24 and PRG4

2020 IEEE Latin America Electron Devices Conference (LAEDC)

Producción CientíficaThree topologies of TiN/Ti/HfO 2 /W resistive switching memories (RRAM) are proposed in this work: crossbar, isolated and isolated-crossbar configurations. All configurations use the same sequence of technological processes. The different topologies are obtained by customizing the layouts corresponding to the bottom electrode (W), and the silicon oxide layer that is deposited on the bottom electrode. A comparative study of the resistive switching mechanisms in the three configurations has been carried out. DC current-voltage cycles and small signal conductance memory maps of single RRAM show relevant differences among the three topologies. Complex structures containing various devices (series, anti-series, parallel, antiparallel) have also been fabricated. Switching loops and memory maps obtained for these complex structures demonstrate that they are fully operative, validating the technological route to manufacture complete RRAM memory chips.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (grants TEC2017-84321- C4-1-R and TEC2017-84321-C4-2-R

Performance Assessment of Amorphous HfO2-Based RRAM Devices for Neuromorphic Applications

Producción CientíficaThe use of thin layers of amorphous hafnium oxide has been shown to be suitable for the manufacture of Resistive Random-Access memories (RRAM). These memories are of great interest because of their simple structure and non-volatile character. They are particularly appealing as they are good candidates for substituting flash memories. In this work, the performance of the MIM structure that takes part of a 4 kbit memory array based on 1-transistor-1-resistance (1T1R) cells was studied in terms of control of intermediate states and cycle durability. DC and small signal experiments were carried out in order to fully characterize the devices, which presented excellent multilevel capabilities and resistive-switching behavior.Ministerio de Ciencia, Innovación y Universidades (Grant, TEC2017-84321-C4-2-R )Fondos Feder y la Deutsche Forschungsgemeinschaft (German Research Foundation) ( with Project-ID 434 434 223- SFB1461)The Federal Ministry of Education and Research of Germany under (grant number 16ES1002

Atomic layer deposited nanolaminates of zirconium oxide and manganese oxide from manganese(III)acetylacetonate and ozone

Producción CientíficaAtomic layer deposition method was used to grow thin films consisting of ZrO2 and MnOx layers. All depositions were carried out at 300 ºC. Some deposition characteristics of the manganese(III)acetylacetonate and ozone process were investigated, such as crystallinity and the dependence of growth rate on the deposition temperature. All films were partly crystalline in their as-deposited state. Zirconium oxide contained cubic and tetragonal phases of ZrO2, while the manganese oxide was shown to consist of cubic Mn2O3 and tetragonal Mn3O4 phases. All the films exhibited nonlinear saturative magnetization with hysteresis, as well as resistive switching characteristics.Fondo Europeo de Desarrollo Regional (projects TK134 and TK141)Ministerio de Economía, Industria y Competitividad (project TEC2017-84321-C4-2-R)Estonian Research Agency (projects PRG4 and PRG753