Unipolar Mode Research Articles

Characteristics of the induced voltage between deep brain stimulation (DBS) device electrodes by a transcranial magnetic stimulation (TMS) device

The combination of deep brain stimulation (DBS) and transcranial magnetic stimulation (TMS) is expected to provide additional insights into the pathophysiology of some brain diseases. However, when using TMS in patients with DBS implants, the induced voltage between DBS electrodes presents the greatest risk of brain damage. This paper describes the characteristics of the induced DBS electrode voltage due to TMS. We first examined the TMS stimulus signal and the DBS output impedance characteristics, and then experimentally investigated the induced DBS electrode voltage for various DBS and TMS conditions. The results show that many factors impact the induced electrode voltage. The induced electrode voltage with DBS device working in the unipolar mode is greater than that with DBS device working in the bipolar mode. No matter DBS device is turned on or turned off, the induced electrode voltage is almost the same, but it can provide a significant addition to the original stimulus waveform. There are no significant differences in the induced DBS electrode voltage when the DBS system is working at different stimulus intensities. Lowering the TMS stimulus intensity could effectively reduce the induced DBS electrode voltage. The induced electrode voltage is also strongly related to the position of the TMS coil relative to the DBS lead. This study provides further information about the characteristics of the induced DBS electrode voltage in TMS applications and a reference for the combined use of DBS and TMS.

Stabilization of ion beam generation in a diode with self-magnetic insulation in double-pulse mode

AbstractThe paper presents the results of statistical studies of ion beam generation in different geometry diodes with explosive emission cathode in a mode of self-magnetic insulation. The experiments were carried out using the TEMP-4M pulsed ion beam accelerator during its operation in both unipolar pulse mode (100 ns, 250–300 kV) and bipolar-pulse mode with the first negative (300–600 ns, 100–150 kV) followed by a second positive (120 ns, 250–300 kV) pulse. It is found that the standard deviation of the total energy and energy density of the beam does not exceed 10–11%, while the same shot-to-shot variation in ion current density was found to be 20–30%. The mechanism of the energy density stabilization from pulse to pulse may be associated with the charge exchange between accelerated ions and stationary molecules and formation of accelerated neutrals. We observed a high correlation between the energy density (or total beam energy) and the duration of the first voltage pulse. We performed analysis of Blumlein statistical performance when the Blumlein was terminated with a resistive load and with a self-magnetically insulated ion diode. A characteristic feature of Blumlein operation in the double-pulse mode is an excellent reproducibility of breakdown of the preliminary spark gap, the variation in breakdown voltage is <2%. At the same time, the shot-to-shot variation in the breakdown voltage of the main spark gap in both bipolar- and unipolar pulse mode is 3–4 times higher than that for the preliminary spark gap. To improve the statistical performance of the main spark gap we used the first voltage pulse at the output of Blumlein to trigger the main spark gap. The new trigatron-type regime of the main spark gap operation showed a better reproducibility of the first pulse duration, with the time jitter not exceeding 10 ns in a set of 50 pulses.

Comparative Analysis of Cascadeded Multilevel Inverter for Phase Disposition and Phase Shift Carrier PWM for Different Load

This paper presents the optimized harmonic elimination stepped waveform technique to improve the output waveform of 7-level Cascaded Multilevel Inverter (CMLI) fed induction motor. The CMLI with separate DC source is used generate a 7-level output with three H-bridge and 12 switch's. The working of 7-level CMLI is analyzed by phase disposition and phase shifting pulse width modulation with bipolar and unipolar modes of operation. The performance of CMLI is examined by various parameters such as THD, power factor, motor current, motor speed and torque. The presented result carried out using MATLAB/simulink. The simulation result for phase disposition and phase shift carrier PWM were compared. The 7-level CMLI hardware with phase shift carrier modulation was developed to validate simulation result.

Resistive switching: An investigation of the bipolar–unipolar transition in Co-doped ZnO thin films

In order to investigate the resistive switching effect we built devices in a planar structure in which two Al contacts were deposited on the top of the film and separated by a small gap using a shadow mask. Therefore, two samples of 10% Co-doped ZnO thin films were sputtered on glass substrate. High resolution X-ray diffraction (HRXRD) revealed a highly c-axis oriented crystalline structure, without secondary phase. The high resolution scanning electron microscopy (HRSEM) showed a flat surface with good coverage and thickness about 300nm. A Keithley 2425 semiconductor characterization system was used to perform the resistive switching tests in the bipolar and unipolar modes. Considering only the effect of compliance current (CC), the devices showed a purely bipolar behavior since an increase in CC did not induce a transition to unipolar behavior.

Thoracic spinal cord stimulation for low back pain in a patient with permanent pacemaker.

Sir, Spinal cord stimulation (SCS) for chronic pain management involves placement of epidural electrodes, which could theoretically evoke device-to-device interference in patients with a permanent cardiac pacemaker (PPM).[1] We report a case of a 52-year-old female patient with double-chamber Medronic Kappa KDR903® device with sensor accelerator-DDDR (Medtronic Inc., Minneapolis, MN, USA/compatible with bipolar diathermy) due to complete heart block, who underwent SCS implantation for treatment of severe chronic low back pain. Several oral analgesic regimens, non-invasive (hydro/physiotherapy) or minimal invasive (electro- acupuncture (EA)) treatment methods had been tested previously unsuccessfully or with extremely short duration of pain relief (24–36 h pain-free period after EA). Therefore, after consultation with a cardiologist, due to patient's history, she was deemed to be a good candidate for SCS. SCS implantation was carried out in the operating theatre under monitored anaesthesia care (MAC) with the patient in the prone position. Standard intraoperative monitoring included continuous electrocardiograph, intermittent non-invasive blood pressure monitoring (every 5 min), capnometry trend (CO2 sensor was attached inside the oxygen mask), and pulse oximetry. MAC was achieved by intermittent intravenous midazolam administration (0.05–0.1 mg/kg). An electrode lead was inserted with its tip at T9 level under real-time X-ray guidance (C-arm fluoroscopy unit). Correct electrode positioning produced paraesthesiae in low back during intraoperative test stimulation corresponding to patient's pain location. Initially, SCS device was programmed at a pulse rate of 80 Hz, a pulse width of 210 μs and an output voltage of 1.2 mV. Pacemaker sensitivity and possible device interference were tested in detail by a Medtronic technician perioperatively. During the trial period, SCS output voltage was increased to the maximum level tolerated by the patient to reveal any possible interference; and no interference was noted. After that, SCS was reset to the clinically chosen parameters mentioned before. Moreover, SCS amplitude was programmed to prevent possible overstepping of the tested safe upper energy level. After 2 days, permanent SCS implantation ensued following the above-mentioned safety measures. After 1 week, an X-ray revealed that the electrode tip had slipped from level T9 to T11. Therefore, SCS was reprogrammed to produce paraesthesiae in patient's pain location at a higher pulse width of 330 μs, whereas the rate and output voltage remained (80 Hz/1.2 mV). Re-interrogation of the pacemaker continued to reveal no interference. One week later, the patient was discharged and SCS device could be switched on and off and the energy level could be increased and decreased by the patient (within preset safe limits). Post-implantation follow-up (at 3–6–12 months) revealed significant pain relief, improvement of basic movement's performance and quality of life as these were documented according to appropriate scales used. This is a report of a safe and effective SCS implantation in a patient with PPM. Despite the theoretical risk of device-to-device interference in such a setting, there are several literature studies describing cases without any interference.[234] The only report of PPM-SCS interference was a case where both devices were used in the unipolar mode and PPM function was inhibited when SCS stimulation amplitude exceeded 1.9–2 mV.[4] Other literature reports of inter-device interference describe cases of simultaneous use of implantable cardioverter defibrillators (ICDs) and SCS, and due to the different behaviour of ICDs compared to PPMs they are not discussed further.[45] According to relevant literature, it seems that there are minimal chances of inter-device interference when both devices use bipolar mode.[2] Despite the fact that in our case, SCS and PPM were used simultaneously with safety and effectiveness, individual testing under careful monitoring is mandatory. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Effect of ultraviolet illumination on metal oxide resistive memory

We investigate the photoelectrical and resistive switching properties of Pt/ZnO/Pt capacitor operated in unipolar mode under ultraviolet (UV) illumination. The oxygen photodesorption under UV illumination explains the photoconduction observed in initial and high resistance states. Meanwhile, oxygen readsorption at surface-related defects justifies the different photoresponses dynamics in both states. Finally, UV illumination significantly reduces the variations of resistance in high resistance state, set voltage and reset voltage by 58%, 33%, and 25%, respectively, stabilizing Pt/ZnO/Pt capacitor. Our findings in improved switching uniformity via UV light give physical insight into designing resistive memory devices.

Resistance switching mode transformation in SrRuO3/Cr-doped SrZrO3/Pt frameworks via a thermally activated Ti out-diffusion process.

This work reports on a mechanism for irreversible resistive switching (RS) transformation from bipolar to unipolar RS behavior in SrRuO3 (SRO)/Cr-doped SrZrO3 (SZO:Cr)/Pt capacitor structures prepared on a Ti/SiO2/Si substrate. Counter-clockwise bipolar RS memory current-voltage (I–V) characteristics are observed within the RS voltage window of −2.5 to +1.9 V, with good endurance and retention properties. As the bias voltage increases further beyond 4 V under a forward bias, a forming process occurs resulting in irreversible RS mode transformation from bipolar to unipolar mode. This switching mode transformation is a direct consequence of thermally activated Ti out-diffusion from a Ti adhesion layer. Transition metal Ti effectively out-diffuses through the loose Pt electrode layer at high substrate temperatures, leading to the unintended formation of a thin titanium oxide (TiOx where x < 2) layer between the Pt electrode and the SZO:Cr layer as well as additional Ti atoms in the SZO:Cr layer. Cross-sectional scanning electron microscopy, transmission electron microscopy and Auger electron spectroscopy depth-profile measurements provided apparent evidence of the Ti out-diffusion phenomenon. We propose that the out-diffusion-induced additional Ti atoms in the SZO:Cr layer contributes to the creation of the metallic filamentary channels.

Correlation between plasma electrolytic oxidation treatment stages and coating microstructure on aluminum under unipolar pulsed DC mode

Alumina coatings were deposited on 6061 aluminum alloy substrates using plasma electrolytic oxidation (PEO) in an alkaline silicate electrolyte. Different electrical parameters, including frequency, duty cycle, and current density were applied to obtain PEO coatings. Scanning electron microscopy (SEM) and microhardness tests were used to investigate the coating microstructure and properties. For each sample, the voltage–time response of the PEO process was obtained and compared with surface morphology, and coating cross sections and thicknesses. Special consideration was given to the connection between the electrical parameters, different stages of the PEO process, and the morphology and microstructure of the coatings. Applying different electrical parameters changed the duration and ratio of the PEO stages in the voltage–time response curve and affected the growth rate, surface morphology, microstructure and microhardness of the coatings. We report the new finding of a correlation between the stage of the PEO process and the microstructure and morphology of the coating.

Failure of communication and capture: The perils of temporary unipolar pacing system

We present a case of a patient with pacemaker dependence secondary to complete heart block who developed loss of capture of her temporary pacemaker. Patient developed torsades de pointes then ventricular fibrillation, requiring CPR and external cardioversion. After patient was stabilized, it was noticed that loss of capture of pacemaker corresponded with nursing care, when the pulse generator was lifted off patient׳s chest wall, and that patient׳s temporary pacing system had been programmed to unipolar mode without knowledge of attending cardiologist. This case highlights the importance of communication ensuring all caregivers are aware of mode of the temporary pacing system.

Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: Computer modelling comparing bipolar and unipolar modes

Purpose: The aim of this study was to compare the efficacy of bipolar (BM) vs. unipolar (UM) mode of radiofrequency ablation (RFA) in terms of creating transmural lesions across the interventricular septum (IVS) and ventricular free wall (VFW).Materials and methods: We built computational models to study the temperature distributions and lesion dimensions created by BM and UM on IVS and VFW during RFA. Two different UM types were considered: sequential (SeUM) and simultaneous (SiUM). The effect of ventricular wall thickness, catheter misalignment, epicardial fat, and presence of air in the epicardial space were also studied.Results: Regarding IVS ablation, BM created transmural and symmetrical lesions for wall thicknesses up to 15 mm. SeUM and SiUM were not able to create transmural lesions with IVS thicknesses ≥12.5 and 15 mm, respectively. Lesions were asymmetrical only with SeUM. For VFW ablation, BM also created transmural lesions for wall thicknesses up to 15 mm. However, with SeUM and SiUM transmurality was obtained for VFW thicknesses ≤7.5 and 12.5 mm, respectively. With the three modes, VFW lesions were always asymmetrical. In the scenario with air or a fat tissue layer on the epicardial side, only SiUM was capable of creating transmural lesions. Overall, BM was superior to UM in IVS and VFW ablation when the catheters were not aligned.Conclusions: Our findings suggest that BM is more effective than UM in achieving transmurality across both ventricular sites, except in the situation of the epicardial catheter tip surrounded by air or placed over a fat tissue layer.

Improvement in the statistical operation of a Blumlein pulse forming line in bipolar pulse mode.

The paper presents the results of studies on shot-to-shot performance of a water Blumlein pulse forming line of 1-1.2 kJ of stored energy. The experiments were carried using the TEMP-4M pulsed ion beam accelerator during its operation in both unipolar pulse mode (150 ns, 250-300 kV) and bipolar-pulse mode with the first negative (300-600 ns, 100-150 kV) followed by a second positive (120 ns, 250-300 kV) pulse. The analysis was carried out for two cases when the Blumlein was terminated with a resistive load and with a self-magnetically insulated ion diode. It was found that in bipolar pulse mode the shot-to-shot variation in breakdown voltage of a preliminary spark gap is small, the standard deviation (1σ) does not exceed 2%. At the same time, the shot-to-shot variation in the breakdown voltage of the main spark gap in both bipolar-pulse and unipolar pulse mode is 3-4 times higher than that for the preliminary spark gap. To improve the statistical performance of the main spark gap we changed the regime of its operation from a self-triggered mode to an externally triggered mode. In the new arrangement the first voltage pulse at the output of Blumlein was used to trigger the main spark gap. The new trigatron-type regime of the main spark gap operation showed a good stability of breakdown voltage and thus allowed to stabilize the duration of the first pulse. The standard deviation of the breakdown voltage and duration of the first pulse did not exceed 2% for a set of 50 pulses. The externally triggered mode of the main gap operation also allowed for a decrease in the charging voltage of the Blumlein to a 0.9-0.95 of self-breakdown voltage of the main spark gap while the energy stored in Marx generator was decreased from 4 kJ to 2.5 kJ. At the same time the energy stored in Blumlein remained the same.

Multi-scale quantum point contact model for filamentary conduction in resistive random access memories devices

We depart from first-principle simulations of electron transport along paths of oxygen vacancies in HfO2 to reformulate the Quantum Point Contact (QPC) model in terms of a bundle of such vacancy paths. By doing this, the number of model parameters is reduced and a much clearer link between the microscopic structure of the conductive filament (CF) and its electrical properties can be provided. The new multi-scale QPC model is applied to two different HfO2-based devices operated in the unipolar and bipolar resistive switching (RS) modes. Extraction of the QPC model parameters from a statistically significant number of CFs allows revealing significant structural differences in the CF of these two types of devices and RS modes.

Coexistence of unipolar and bipolar resistive switching in Pt/NiO/Pt

We demonstrate the coexistence of unipolar and bipolar resistive switching in NiO thin film fabricated by reactive sputtering. It was shown that the required voltages for switching operations in the bipolar switching mode are smaller than the voltages in the unipolar mode, while the ON/OFF resistance levels are similar for the two modes. The NiO resistive switching device also exhibited transitions between the two switching modes, with the subsequent I-V characteristics unaffected by the switching history, which clearly indicates that the two switching mechanisms are directly related. The switching versatility in NiO is expected to facilitate improved device performance, for example, by increasing the margin of programming voltages. Based on the investigation of device characteristics, we discuss the switching processes for the two switching modes and their relationship.

Bipolar and unipolar resistive switching modes in Pt/Zn0.99Zr0.01O/Pt structure for multi-bit resistance random access memory

In this work, we report the coexistence of bipolar resistive switching (BRS) and unipolar resistive switching (URS) modes in Pt/Zn0.99Zr0.01O/Pt structure device. After the forming process, this device with URS behavior exhibits either URS mode in the same direction or BRS mode in the opposite direction during the reset process. Controllable multi-state resistances in the low and high resistance states for the BRS mode were obtained by imposing different compliance currents (Icc) and the span of voltage sweeping in the reset process (Vstop). These results suggest that our devices have high potential for the next generation of nonvolatile memory applications.

Temperature dependence of resistance of conductive nanofilament formed in Ni/NiOx/Pt resistive switching random access memory

We investigated the resistive switching characteristics and temperature dependence of resistance of a Ni/NiOx/Pt resistive switching memory. The device was operated in a unipolar operation mode. From the temperature dependence of resistance, it is suggested that the conduction mechanism of the low-resistance state is metallic. Moreover, a deformed site that may correspond to the conductive filament appeared after the forming process. Cross-sectional transmission electron microscopy with energy dispersive X-ray analysis showed that the Ni atomic content at the NiOx of the deformed area was larger than those of other areas. It is strongly suggested that the conductive filament formed in the NiOx layer is composed of Ni atoms.

Characteristic Evolution From Rectifier Schottky Diode to Resistive-Switching Memory With Al-Doped Zinc Tin Oxide Film

We demonstrate a metal sandwiched Al-doped zinc tin oxide (AZTO) thin-film device to exhibit a characteristic evolution process from Schottky junction diode to resistive-switching random access memory (RRAM) applications. The proposed TiN/Ti/AZTO/Pt device can initially show good rectifying characteristics and high forward-bias current for Schottky diodes. After applying with an electrically triggered forming process, the transition of electrical behavior occurs and evolves from the diode to RRAM characteristics. The RRAM device exhibits the coexistence of bipolar and unipolar resistive-switching modes through the positive-bias forming and reversed-bias forming process, respectively. In addition, the RRAM device with bipolar mode can perform the functionality of multilevel cell storage, while the one with unipolar mode shows stable resistive-switching performance. Furthermore, one-transistor and one-resistor (1T1R) architecture with an RRAM cell connected with a thin-film transistor (TFT) device is developed in this paper. The TFT device using AZTO film as an active channel layer performs good electrical characteristics for a driver in the 1T1R operation scheme. The integration of AZTO-based electronic devices has great potential for increasing the application diversity of metal oxide AZTO thin film as well as the flexibility of circuit design in the emerging optoelectronic technologies.

Effect of duty cycles on the deposition and characteristics of high power impulse magnetron sputtering deposited TiN thin films

High power impulse magnetron sputtering (HiPIMS) is a novel physical vapor deposition (PVD) technique. HiPIMS is a low-temperature process, giving well-adherent coatings, better quality films, and droplet-free deposition. It provides enhanced gas dissociation and highly ionized plasma by inputting a high power during short pulses to the target. The target material is therefore not only sputtered but also ionized during the deposition process. In this study, TiN thin films were deposited using a uni-polar mode HiPIMS process. Nitrogen was used as the reactive gas to deposit TiN along with Ar gas. The deposition of TiN films was investigated by varying the duty cycles from 2 to 10% to have peak power density ranging from 208 to 1064W/cm2. A high peak power density was obtained at a low duty cycle. DC magnetron sputtered TiN thin film (duty cycle=100%) was also deposited for comparison. We demonstrate that the HiPIMS deposited TiN thin film exhibits a denser structure and smoother surface at low duty cycles. It was also found that the intense ion bombardment at low duty cycles deteriorates the film structure and their mechanical properties. Moderate ion bombardment at a duty cycle of 4.5% gives the highest (111)/(200) intensity ratio and the highest amount of TiN bonding. This results in a film having the highest hardness, elastic modulus, and corrosion resistance of 29.3GPa, 388.2GPa, and 1.56E+06 (Ω/cm2), respectively. However, oxygen was found in the resulting films.

Electrodeposition of iron-molybdenum coatings from citrate electrolyte

Specific features of the electrodeposition of iron-molybdenum coatings from a citrate electrolyte based on iron(III) sulfate and sodium molybdate in dc and unipolar pulsed modes were studied. It was demonstrated that bright compact coatings with varied content of molybdenum can be produced by varying the relative concentrations of salts of the alloy-forming components and the solution pH. The current density ranges providing the high efficiency of the galvanostastic electrolysis were determined and it was shown that using the pulsed mode makes smaller the amount of nonmetallic impurities in a coating, diminishes its roughness and leads to formation of surface layers with a more uniform composition, The iron-molybdenum coatings exhibit a high corrosion resistance in corrosive media and physicomechanical properties improved as compared with the base metal, which makes it possible to recommend these coatings for protection from corrosive-mechanical disintegration and restoration of the surface of worn articles.

Amorphous SiC based non-volatile resistive memories with ultrahigh ON/OFF ratios

Amorphous SiC based resistive memory Cu/a-SiC/Au devices were fabricated and their resistive switching characteristics investigated. Co-existence of bipolar and unipolar behavior has been observed with ON/OFF current ratio in the range of 108–109. These high ratios are due to the conduction in the OFF state being dominated by the Schottky barrier between the Au and SiC. ON/OFF ratios exceeding 107 over 10years were predicted from retention characterization. The unique performance combination of the extremely high ON/OFF ratio, coexistence of bipolar and unipolar switching modes as well as excellent stability and retention suggest significant application potentials of Cu/a-SiC/Au RM devices.

Developments of SiC DioMOS (Diode Integrated SiC MOSFET)

ABSTRACTSiC power devices can handle large power and high frequency switching beyond the Si power devices. Typical full-SiC power modules are composed of both SiC-MOSFETs and SiC-SBDs to suppress the degradation of Ron of SiC-MOSFET during the bipolar reverse-current flow while there will be unfavorable consequences such as increased material cost, larger area, and larger wiring inductances. Panasonic has proposed the SiC-DioMOS which successfully integrates the unipolar reverse diode without any increase of chip size from the original DIMOS transistor. The SiC-DioMOS utilizes the highly-doped n-type epitaxial channel under the MOS gate for the FET channel and also for the reverse conduction path of the diode. Thickness and concentration of the highly-doped n-typed channel are carefully designed to achieve reasonable Vth of the MOSFET and Vf0 barrier constituting the diode current. The MOSFET and also the MOS-channel diode completely operate under unipolar mode. The SiC-DioMOS with BVds=1700V, Ron=20mΩ、Vth=4.5V, Vf0=0.8V is successively fabricated using the state-of-the-art epitaxial-growth technique. Fast switching of tr=58ns and tf=13ns is confirmed. The SiC-DioMOS meets practical standards for safety operation of high-power fast switching without SiC-SBD.