Application Of Voltage Pulses Research Articles

Rapid threshold switching dynamics of co-sputtered chalcogenide Ge15Te85 device for selector application

Threshold switching is a unique characteristic feature in amorphous chalcogenide materials that establishes stable and fast switching between a high resistance OFF state and a conductive ON state in the amorphous phase, envisaging the electronic nature of two-terminal ovonic threshold switch (OTS) selectors in vertically stackable cross-point memory arrays. In this paper, we demonstrate voltage-dependent nanosecond threshold switching dynamics and stable OFF–ON transitions of co-sputtered thin Ge15Te85 film devices using ultrafast time-resolved current–voltage measurements. The time-resolved measurement of device current upon the application of voltage pulse reveals a stable threshold switching and OFF–ON transient characteristics of OTS devices and the measured delay time is found to decrease to few nanoseconds upon increasing the amplitude of the applied voltage pulse and such OTS characteristics are found to be stable even above 60% of the high value of threshold voltage. These experimental results found to be consistent with analytical solutions and also demonstrate a systematic trend in the voltage dependent switching properties enabling ultrafast threshold switching characteristics suitable towards designing reliable and stable OTS selector devices.

Sleep-Dependent Memory Consolidation in a Neuromorphic Nanowire Network.

A neuromorphic network composed of silver nanowires coated with TiO2 is found to show certain parallels with neural networks in nature such as biological brains. Owing to the memristive properties emerging at nanowire-to-nanowire contacts, where the Ag/TiO2/Ag interface exists, the network can store information in the form of connectivity between nanowires in the network as electrically measured as an increase in conductance. The observed memory arises from an interplay between the topological constraints imposed by a complex network structure and the plasticity of its constituting memristive Ag/TiO2/Ag junctions. Regarding the long-term decay of the connectivity in the network, we further investigate the controllability of the established connectivity. Inspired by the regulated activity cycles of the human brain during sleep, a learning-sleep-recovery cycle was mimicked by applying voltage pulses, with controlling pulse heights and duty ratios, to the nanowire network. Interestingly, even when the conductance was lost during sleep, the network could quickly recover previous states of conductance in the recovery process after sleep. Comparison between results of experiments and theoretical simulations revealed that such a quick recovery of conductance can be realized by sparse voltage pulse application during sleep; in other words, sleep-dependent memory consolidation occurs and can be controlled. The present results provide clues to new learning designs in neuromorphic networks for achieving longer memory retention for future neuromorphic technology.

Auxiliary capacitor to enhance oscillation in circuit and reduce current onset delay in HiPIMS discharge: Theory, experiment and simulation

In high power impulse magnetron sputtering (HiPIMS) discharge, generally, the current onset lags the applied pulse voltage by a significant time which can reach to several tens of microseconds, especially at a low gas pressure. The existence of this delay will affect the instantaneous and average power, and in turn, it determines the plasma dynamics and the thin film properties. The origin of current onset delay can be traced back to gas breakdown in E × B fields. This work firstly focuses on the theory and model of gas breakdown in the HiPIMS discharge with parallel electrodes. Theoretically, the breakdown voltage of argon in HiPIMS is about −700 V at gas pressure of 0.45 Pa, while it can exceed −1100 V at pressure of 0.4 Pa. To operate the HiPIMS at a low pressure with a short delay time of current onset, the means using an auxiliary capacitor C connected in parallel with plasma between electrodes to enhance oscillation in circuit (named ECO-HiPIMS) is employed, which can generate a high oscillation voltage during the gas breakdown phase. Choosing a suitable capacitor, this oscillation voltage reaches up to −1322 V at applied pulse voltage of −700 V, and in turn, the delay time can be shortened from around 50 μs (in standard HiPIMS) to less than 5 μs. Finally, the plasma dynamics during gas breakdown phase in HiPIMS and ECO-HiPIMS has been investigated by a two-dimension particle in cell/Monte Carlo (2D PIC-MCC) simulation.

Compensation Charge Control and Modeling for Reproducing Negative Capacitance Effect of Hafnia Ferroelectric Thin Films

AbstractTo enable continuing development of the performance of highly integrated semiconductor chips, it is necessary to dramatically lower the power consumption of transistors. The discovery of the negative capacitance (NC) effect and the ferroelectric properties of HfO2 thin films have raised the possibility of surpassing the known physical limitations of the 60 mV subthreshold slope of the current MOSFETs. However, for commercial application, stable reproducibility of the voltage drop effect due to the ferroelectric polarization and a model that can fully interpret this phenomenon must be obtained. Despite intense recent efforts, guidance for the design of devices for mass production based on the NC effect is currently unavailable. This study has directly observed the NC effect and confirmed that the NC effect can be controlled through analysis based on the equivalent circuit theory. It is experimentally verified that the NC effect is caused by an imbalance between the amount of polarization switching and the amount of charge supplied to compensate for such switching in the initial stage of the applied voltage pulse. The results suggest that a gate structure or peripheral circuit that can actively respond to polarization switching is necessary to implement a novel MOSFET with breakthrough power consumption.

Time-resolved in situ measurements and predictions of plasma-assisted methane reforming in a nanosecond-pulsed discharge

This study investigates the plasma properties and chemical kinetics of plasma-assisted methane reforming in a He diluted nanosecond-pulsed plane-to-plane dielectric barrier discharge (ns-DBD) through the combination of time-resolved in situ laser diagnostics and a 1-D numerical model. Plasma-assisted fuel reforming kinetic mechanisms have predominantly been evaluated on the basis of matching reactant conversion and syngas production to steady-state measurements, which cannot describe the full range of chemistry and physics necessary to validate the model. It was found that adding 1% CH4 to a pure He ns-DBD led to a faster breakdown along the rising edge of the applied voltage pulse, thereby lowering the reduced electric field (E/N), electron number density, and electron temperature. Further addition of CH4 did not continue to alter the E/N in the model. Laser absorption spectroscopy was used to measure gas temperature, C2H2, H2O, and CH2O in a CH4/CO2/He discharge to serve as validation targets for the predicted reaction pathways. CH2O was predicted within 25% of the measured value, while H2O and C2H2 were under-predicted by a factor of two and three, respectively. From path flux analysis, the major pathway for CH2O formation was through the reaction between CH3 and O, while C2H2 formation had multi-step pathways that relied on ions like CH3+ and C2H5+. The path flux analysis also shows that CH2 is a significant intermediate for production of both CH2O and C2H2, and increased CH2 concentration could improve model predictions. The results show that the use of reaction rate constants with lower uncertainties and inclusion of He2+ are needed to improve the predictions. Finally, varying the ”equivalence ratio”, defined by the CH4 dry reforming reaction to H2 and CO, from 0.5 to 2 was shown to have a weak effect on measured product species and experimental trends were explained based on pathways extracted from the model.

Controlling the resistive switching hysteresis in VO2 thin films via application of pulsed voltage

We investigate the origin of the variation in resistive switching hysteresis of VO2 thin films. Using pulsed electrical measurements in textured VO2 thin film devices, we show that the hysteresis observed in I–V curves results from Joule heating effects, particularly in the low-resistance state. The hysteresis is reduced by increasing the cooling time between pulses. Based on a mechanism of Joule heating-induced metal-insulator transition, numerical simulations are performed, which agree with the experimental variation in the hysteresis. Finally, a framework for engineering the I–V curves of VO2 devices is proposed.

Reversible phase-transition control in nanometer-sized zirconium wires via pulse-voltage impression

Pulse-voltage-stimulated phase transition in nanometer-sized zirconium (Zr) wires was observed in situ by high-resolution transmission electron microscopy. Simultaneously, the variation in conductance during the transition between crystalline and amorphous phases was examined. The crystalline phase of a hexagonal closed-packed structure in the wires transformed into an amorphous phase while applying pulse voltages of 4 ns in width, and subsequently returned to the initial crystalline phase by the impression of pulse voltages of 5 ms in width; the reversible phase transition via voltage impression using shorter and longer pulse waves was observed. The average conductance per a unit area in the amorphous phases was decreased to 0.87 of the crystalline phases. The amorphous region in the wires expanded gradually by every pulse-voltage impression, whereas the conductance decreased stepwise in response to the gradual expansion. It was demonstrated that the conductance of the wires can be controlled in a stepwise manner via pulse-voltage impression, leading to the application of the nanowires to functional nanodevices.

Fabrication of GaOx based crossbar array memristive devices and their resistive switching properties

Memristive devices attract much attention for the application to neuromorphic computing. Here we focus on amorphous GaOx based memristive devices and their integration as a crossbar architecture which is mandatory to improve parallelism in computing and essential to future power-saving, high-speed and reliable artificial neural networks (ANN). Fabricated Pt/GaOx/ITO crossbar array memristive devices with 3 × 3 μm2 crosspoints exhibit non-filamentary reversible bipolar resistive switching (RS) without any electroforming processes. We demonstrate the gradual resistance change by repeating voltage sweep and applying pulse voltages. The expression of spike-timing-dependent plasticity property, one of synaptic functions in neuromorphic devices, is also successful in the present device. The obtained results strongly suggest that the drift of oxygen vacancies in GaOx plays an important role in the RS behavior and the GaOx based crossbar array memristive devices have a great potential for hardware implementation of ANN.

(Invited) Current and Voltage Control of Intermediate States in Bipolar Rram Devices for Neuristor Applications

Nowadays, there is an increasing interest in the fabrication of neuristors in which memristors are used to create a neuron-like behavior (1). Memristors based on resistive switching memories (RRAM) are promising candidates to implement artificial synaptic devices for their use in neuromorphic systems, due to their high number or reachable conductance levels.In a previous work (2) we show that TiN/Ti/ HfO2/W capacitors exhibit resistive switching behavior and that intermediate conductance states can be obtained by varying the voltage applied to the device (Voltage-control mode, VCM). We demonstrated that the conductance values vary near linearly when applying voltage depression pulses. During depression process, the conductance state depends on the amplitude and the duration of the voltage pulses length. Moreover, this process is accumulative: the conductance decreases when applying successive pulses of same amplitude and length. In contrast, the potentiation characteristic is not linear, as for other synaptic devices, as PRAMs: the transitions from high resistance state (HRS) to low resistance state (LRS) is very sharp and intermediate conductance state cannot be controlled. Decreasing the voltage pulse length or amplitude was not a choice. Additionally, we tried to use ramps where the voltage linearly increases and once again the characteristics remain very nonlinear. In summary, a very poor control of the potentiation state is obtained when using voltage as synapse stimulus.In the present work, we demonstrate that the potentiation process can be linearly controlled when using current as the synapse stimulus (Current-control mode, CCM).The devices used in this work are TiN/Ti/10-nm HfO2/W MIM capacitors. The high-k dielectric was deposited by the atomic layer deposition (ALD) technique at 225 ºC using TDMAH and water as hafnium and oxygen precursors respectively. Nitrogen was used as carrier and purge gas. The bottom electrode consists of a 200 nm W layer, and the top electrode consists of a 200 nm TiN layer and a 10 nm Ti layer. Metal electrodes were deposited by magnetron sputtering.An HP 4155B Semiconductor Parameter Analyzer was used to perform the voltage and the current measurements. In order to perform the pulsed measurements, we used an Agilent 33500B Series waveform generator which provides voltage pulses and ramps. The voltage waveforms are converted to mimic current waveforms using a home-made voltage to current converter. All the measurements were carried out at room temperature and the entire experimental setup was computer controlled.In figure 1 we show that the conductive path formation (electroforming) requires a very few nA current value. As the filament is formed, the devices reaches the low resistance state (LRS) and the voltage falls to a very low value. Once the filament is formed, we have measured the voltage-current (V-I) characteristic instead of the more usual current-voltage (I-V) characteristic. Figure 2 shows 50 consecutive bipolar switching V-I loops. It is important to point that in the CCM mode, a voltage compliance in the reset transition has to be used. Otherwise, irreversible oxide breakdown takes place due to the huge increase of the structure dissipated power. Departing from the HRS state we have applied current pulses of increasing amplitude. In Fig. 3 we plot the conductance of the device measured at 0.1 mA as a function of the amplitude of the current pulse previously applied. We see that the synaptic potentiation linearly depends on the pulse amplitude in the CCM mode. In Figure 4 we demonstrate that potentiation occurs at the very first current pulse. Successive pulses do not modify the conductance value. In summary, the potentiation process in CCM mode is very fast, non-accumulative and nearly linear. To confirm that this process is very fast we have obtained current transients in the VCM mode (Figure 5) which confirms that when a positive voltage is applied the current increases occurs at very short times (lower than the experimental setup time response).In contrast, the depression process is better controlled by applying voltage pulses (VCM mode) as described in ref. 2. Moreover, the depression process is slower and accumulative. That can be observed in Fig. 6 in which a train of -0.8 V voltage pulses is applied. The conductance decreases from pulse to pulse and show very long time rates (tens of ms for the showed voltage)In conclusion, CCM mode for potentiation and VCM mode for depression characteristic is the optimal combination to control the synaptic behavior of the studied bipolar RRAM devices.References Timmer, Nature Materials, 2012. DOI: 10.1038/NMAT3510García et al., Micr. Eng. 215, 110984 (2019). Figure 1

Vanadium Dioxide for Reconfigurable Antennas and Microwave Devices: Enabling RF Reconfigurability Through Smart Materials

We present a comprehensive study of a new method to reconfigure, tune, and/or program antennas and radio-frequency (RF) devices. The method consists of using electrical signals to induce the solid-tosolid phase transition in vanadium dioxide (VO2) thin-film patterned structures that connect the device metallization layer with extensions, thus effectively changing the geometry of the device. Applied voltage pulses to a resistive heater electrically isolated from the antenna metallization layers increase the temperature of the VO2 strip across the phase transition. Hence, the VO2-biasing mechanism and the antenna are electrically decoupled, which enables an additional degree of freedom for antenna and microwave device engineers as the reconfiguration is no longer restricted by any biasing network limitations. Radiation patterns are also maintained unaffected. This decoupling adds into the design spectrum, applications that require wideband tuning, low-loss structures (e.g., arrays and reflectarrays), and even reconfigurable cloaks. The VO2 switch is arguably the smallest ever used to reconfigure an antenna, which requires further circuit element considerations. The presented method is validated through a series of antenna prototypes that demonstrate VO2 applicability on wire and aperture antennas. Details and challenges of the monolithic integration of VO2 thin films and resistive heaters for reconfigurable antennas, along with the measurement setup, are presented. Results unveil this new reconfiguration technique and suggest further applications, as the VO2 may also be activated optically.

New Grounded and Floating Decremental/Incremental Memristor Emulators Based on CDTA and Its Application

This paper presents grounded and floating memristor emulators based on current differencing transconductance amplifier. These emulators are realized using current differencing transconductance amplifier, operational transconductance amplifier and a grounded capacitor. Incremental to decremental memristor emulators and vice versa are easily obtained by modifying the circuit slightly. These memristor emulators are very simple in design over other complex realizations reported in the literature. The pinched hysteresis curves have been obtained without using analog multiplier for a wide range of frequency that varies from 600 kHz to 2 MHz. The property of retention has been verified for proposed design of memristor emulators after applying voltage pulse of amplitude 100 mV and frequency 1 MHz. Non-ideal analysis including the effects of parasitic impedances on the behaviour of proposed memristor emulators has also been presented. The proposed designs of memristor emulators have been simulated by Mentor Graphics Eldo simulation tool with TSMC 0.18 µm, level 53, CMOS technology parameters. The performance of proposed memristor emulator is verified by embedding it in the realization of current- mode analog filter.

Vacuum electrical breakdown conditioning study in a parallel plate electrode pulsed dc system

Conditioning of a metal structure in a high-voltage system is the progressive development of resistance to vacuum arcing over the operational life of the system. This is, for instance, seen during the initial operation of radio frequency (rf) cavities in particle accelerators. It is a relevant topic for any technology where breakdown limits performance, and where conditioning continues for a significant duration of system runtime. Projected future linear accelerators require structures with accelerating gradients of up to 100 MV/m. Currently, this performance level is only achievable after a multi-month conditioning period. In this work, a pulsed DC system applying voltage pulses over parallel disk electrodes was used to study the conditioning process, with the objective of obtaining insight into its underlying mechanics, and ultimately, to find ways to shorten the conditioning process. Two kinds of copper electrodes were tested: As-prepared machine-turned electrodes ("hard" copper), and electrodes that additionally had been subjected to high temperature treatments ("soft" copper). The conditioning behaviour of the soft electrodes was found to be similar to that of comparably treated accelerating structures, indicating a similar conditioning process. The hard electrodes reached the same ultimate performance as the soft electrodes much faster, with a difference of more than an order of magnitude in the number of applied voltage pulses. Two distinctly different distributions of breakdown locations were observed on the two types of electrodes. Considered together, our results support the crystal structure dislocation theory of breakdown, and suggest that the conditioning of copper in high field systems such as rf accelerating structures is dominated by material hardening.

Visualization of Carrier Transport in Luminescent Polymer Thin Film by Using Transient Photoluminescence Decay Imaging

Transient photoluminescence (PL) decay imaging is conducted for visualizing carrier transport in luminescent polymer semiconductor thin films. The method is simple, but enables a real‐time observation of carrier motion on the scale of several millimeters in luminescent thin films. Decrease in the PL intensity of the channel region in organic field‐effect transistor (OFET) is observed in accordance with the device operation. Upon application of pulse voltages to the source electrode for carrier injection, the transient PL decay motion is visualized using a conventional charge‐coupled device (CCD) camera. By analyzing the PL decay motion, hole and electron mobilities of poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) (F8BT) thin film are evaluated as 1.3 × 10−4 cm2 (V s)−1 and 3.2 × 10−5 cm2 (V s)−1, respectively. Mobility anisotropy is also visualized by using round‐shaped electrode as the source electrode, and the difference of mobility anisotropy for hole and electron of F8BT is clearly identified.

A new type artificial synapse based on the organic copolymer memcapacitor

Abstract A memcapacitor device with a structure of Al/copolymer/ITO is fabricated by an organic donor-acceptor (D-A) copolymer. The device exhibits the bidirectional gradual modulation of the capacitance state, which enables it to simulate the synaptic plasticity. At first, the short-term plasticity (STP) of the synapse is realized in the device, including the paired pulse facilitation (PPF), potentiation and depression behaviors. Then the transition from STP to long-term plasticity (LTP) and the learning-forgetting-relearning behavior of the synapse is achieved by repeatedly applying voltage pulses stimulation. More inspiringly, these synaptic functions are well performed at low operating voltage of 0.1 V, the voltage is reduced by 95% to compare with the previous report. And the sensitivity can reach 50 mV, which is consistent with the action potential producing synaptic plasticity in the human brain. These results provide a powerful reference for the research of high sensitive artificial synapse with low power consumption based on memcapacitor.

Resistive switching and synaptic behaviors of an HfO2/Al2O3 stack on ITO for neuromorphic systems

This work reports on the bipolar resistive switching (RS) characteristics and possible applicability to transparent synaptic devices when an ultrathin Al2O3 interfacial layer is introduced between HfO2 and an indium tin oxide (ITO) bottom electrode for an RS device (TaN/HfO2/Al2O3/ITO). The introduction of the Al2O3 interfacial layer on ITO allows for a more gradual current change during the RESET process. As a result, the bilayer RS device offers multilevel resistance states with reasonable controllability under the application of various DC and pulse voltages. Considering the systematic changes in the resistance in accordance with the negative/positive voltage pulses during the potentiation/depression processes, as well as the reasonable spike-timing-dependent plasticity characteristics, the proposed RS bilayer on ITO is a potential candidate for transparent synaptic devices in neuromorphic systems.

A method of generating random bits by using electronic bipolar memristor**Project supported by the National Natural Science Foundation of China (Grant No. 61832007) and the National Key Research and Development Program of China (Grant No. 2018YFB1003304).

The intrinsic stochasticity of resistance switching process is one of the holdblocks for using memristor as a fundamental element in the next-generation nonvolatile memory. However, such a weakness can be used as an asset for generating the random bits, which is valuable in a hardware security system. In this work, a forming-free electronic bipolar Pt/Ti/Ta2O5/Pt memristor is successfully fabricated to investigate the merits of generating random bits in such a device. The resistance switching mechanism of the fabricated device is ascribed to the electric field conducted electrons trapping/de-trapping in the deep-energy-level traps produced by the “oxygen grabbing” process. The stochasticity of the electrons trapping/de-trapping governs the random distribution of the set/reset switching voltages of the device, making a single memristor act as a random bit in which the resistance of the device represents information and the applied voltage pulse serves as the triggering signal. The physical implementation of such a random process provides a method of generating the random bits based on memristors in hardware security applications.

Electrophysical characteristics of the desalination plant based on the principle of capacitive deionization

The basic electrophysical and technological parameters of a CDI desalination plant designed for long-term operation, based on the principle of salt solution deionization on electrodes with a developed surface, have been studied. The proposed equipment for water demineralization uses a simplified design with pumping the solution through electrodes (“flow through electrodes”), which allows bypassing without relatively expensive ion-exchange membranes. Non-woven felt “Karbopon-V-Aktiv-200-65A” was used as the electrode material, the estimated value of the specific surface of the material of which, according to the results of measurements by the method with the deposition of acetone, amounted to ~ 1000 m2/g or more. Also, the advantages of the proposed CDI desalination plant are the absence of highly loaded power elements, the use of corrosion-resistant materials and the reliability of the electrode stacking scheme, which makes it possible to count on its long-term and reliable operation. Various possibilities of operational adjustment of the desalination plant modes are demonstrated – reduction of the discharge period due to the application of voltage pulses of reverse polarity, increasing efficiency by organizing a procedure for taking into account the real voltage at the working electrodes inside the CDI cell. The high-energy efficiency of demineralization is determined by the relatively low operating voltage of ~ 1 V. It is established that with increasing amperage, salt removal is more efficient, respectively, the degree of desalination is higher at a higher current: the working period of 30 minutes corresponds to the degree of desalination of ~ 20 % at a voltage of 1.4 V and ~ 30 % in the 1.6 V mode. The possibility of increasing the desalination capacity to ~ 100 g of salt over a half-hour period was noted. Possible ways to further improvement of the performance of the equipment presented in the article are identified.

STM induced manipulation of azulene-based molecules and nanostructures: the role of the dipole moment.

Among the different mechanisms that can be used to drive a molecule on a surface by the tip of a scanning tunneling microscope at low temperature, we used voltage pulses to move azulene-based single molecules and nanostructures on Au(111). Upon evaporation, the molecules partially cleave and form metallo-organic dimers while single molecules are very scarce, as confirmed by simulations. By applying voltage pulses to the different structures under similar conditions, we observe that only one type of dimer can be controllably driven on the surface, which has the lowest dipole moment of all investigated structures. Experiments under different bias and tip height conditions reveal that the electric field is the main driving force of the directed motion. We discuss the different observed structures and their movement properties with respect to their dipole moment and charge distribution on the surface.

Enhancing Programming Variability in Multi-Bit Phase Change Memory Cells for Security

We performed gradual programming of phase change memory (PCM) line cells with repeated pulses to transition from the crystalline to the amorphous state through various intermediate states and analyzed the variability in programming trends for different cell shapes and sizes. The crystalline PCM cells experienced sequences of repeated applied voltage pulses of either identical amplitudes or gradually increasing amplitudes. With repeated identical amplitude pulses, large number of pulses (~1,000) were required to reach a full reset of the cells through partial reset and partial set steps. With repeated increasing amplitude pulses, ~20-30 pulses were sufficient to fully reset the cells through gradual partial reset steps. Both programming approaches resulted in significant cell-to-cell variability for all cells, with stronger variability for narrower cells. However, the latter pulsing approach was more practical and resulted in more uniform distribution of all states. The stronger cell-to-cell programming variability for the narrower cells is attributed to the smaller number of crystalline grains in each cell and to the larger relative impact of manufacturing process variations. Statistical analysis of two example data sets shows promise of PCM programming variability for hardware security applications.

Mid-infrared non-volatile silicon photonic switches using nanoscale Ge2Sb2Te5 embedded in silicon-on-insulator waveguides

We propose and numerically analyze hybrid Si-Ge2Sb2Te5 strip waveguide switches for the mid-infrared wavelength of 2.1 μm. The switches investigated are of one input-one output (on-off) and one input-two outputs (directional coupler) types. The reversible transition between the switch states is achieved by inducing phase transition from crystalline to amorphous and vice-versa by application of voltage pulses. The approach of embedding the nanoscale active material Ge2Sb2Te5 within the Si waveguide is taken to enhance the interaction of light with the active region of the switches. The dimensions of the active regions of the switches are optimized to achieve low insertion loss, low switching energy and high extinction ratio. In the case of the on-off switch, an extinction ratio of 33.79 dB along with an extremely low insertion loss of 0.52 dB is achieved using an optimum Ge2Sb2Te5 length of only 0.92 μm. For the directional coupler switch, an extinction ratio of 10.33 dB and 5.23 dB is obtained in the cross and bar states respectively using an active length of 52 μm. These values of extinction ratio, which are otherwise 18.59 dB and 8.33 dB respectively, are due to the necessity of doping the Si beneath the Ge2Sb2Te5 to facilitate the electrical conduction needed for Joule heating. A suitable gap of 100 nm is maintained between the active and passive arm of the directional coupler switch. Electro-thermal co-simulations confirm that phase change occurs in the whole of the Ge2Sb2Te5 region in both types of switches.