22 research outputs found
To Be or Not to Be â Review of Electrical Bistability Mechanisms in Polymer Memory Devices
Get PDFopen access articleOrganic memory devices are a rapidly evolving field with much improvement
in device performance, fabrication, and application. But the reports have been
disparate in terms of the material behavior and the switching mechanisms in
the devices. And, despite the advantages, the lack of agreement in regards to
the switching behavior of the memory devices is the biggest challenge that
the field must overcome to mature as a commercial competitor. This lack
of consensus has been the motivation of this work wherein various works
are compiled together to understand influencing factors in the memory
devices. Different works are compared together to discover some clues
about the nature of the switching occurring in the devices, along with some
missing links that would require further investigation. The charge storage
mechanism is critically analyzed alongside the various resistive switching
mechanisms such as filamentary conduction, redox-based switching, metal
oxide switching, and other proposed mechanisms. The factors that affect
the switching process are also analyzed including the effect of nanoparticles,
the effect of the choice of polymer, or even the effect of electrodes on the
switching behavior and the performance parameters of the memory device
NonâZero and OpenâLoop CurrentâVoltage Characteristics in Electronic Memory Devices
Get PDFopen access articleThis work focuses on the non-zero-crossing and open-loop currentâvoltage (IâV) characteristics of electronic memory devices that are studied and focused on primarily for non-volatile memory storage applications. Gold nanoparticles-based devices are fabricated to understand possible non-crossing zero and open-loop currentâvoltage behavior, where a non-zero current and open loop IâV characteristics are observed at zero voltage. While other studies have attributed this behavior as a âbattery effectâ, this study presents an alternate perspective for non-redox-based charge storage memory devices. The electrical measurements clearly demonstrate that the non-zero current and open-loop characteristics are due to the charge trapping of the gold nanoparticles. The charge accumulation within the nanoparticle is observed to create a non-zero potential within the device and thereby encouraging such behavior, even though the applied external voltage is zero. The longstanding mystery in deciphering if electrical measurements or the charge storage device contributes toward non-zero property is unfurled in this article. A possible charge storage model is proposed and further verified using liquid crystals-based two terminal devices. The presence of internal potential leads to an offset within the devices, a non-zero current and open-loop IâV even when the external applied voltage is zero
A Study on Charge Storage mechanism using gold nanoparticles to understand the Electrical Bistability in two-terminal Organic Memory Devices
Get PDFOrganic electronics has taken leaps and bounds in the past few years. From LED screens to wearable technology, it has enabled the emergence of technologies that would have been unimaginable a few decades earlier. The organic memory devices have emerged to be a perfect alternative in the non-volatile memory sector due to its compatibility in the printed technology, low power application and device performance too. Despite these advantages progress in the field has been slow due to the lack of clarity around the device operation. The field has seen several works that have focussed on the same device or even similar structures, only to arrive in vastly different conclusions. A persistent lack of agreement in this regard, despite some excellent work having been done in the field, point to a gap in knowledge in the physics of the device operation.
The focus of this work has been to address this uncertainty of device operation in two terminal memory devices. This work was focussed on two terminal gold nanoparticle devices that have been fabricated by drop casting on gap cells. The problem definition was based on a literature survey of several work that had been conducted in this area for around two decades. Several mechanisms that were proposed as a result of several investigations have been identified and arranged in a manner to obtain a holistic view of the subject.
Several studies have been investigated closely to recognise gaps in the experiment design and isolate factors that might have contributed to the final result. As a result, gold nanoparticle devices were carefully designed to avoid any parasitic contribution from these external factors. These devices were investigated under varying electric field to study the behavioural response. The result has shown that the device operation relies heavily on the charge storage to bring about a change in the resistance. The device properties were tested by Impedance Spectroscopy measurement, in order to verify if the change in device conduction was due to resistive switching (like filamentary conduction, valence change switching etc.) or due to charge storage. The results demonstrated that the charge storage in the nanoparticles were responsible for the resistance change of the device. This was further confirmed by conducting the impedance measurement on the device at zero-DC-bias after applying a non-zero bias to measure the remnant charge that are trapped in the devices. These tests revealed the presence of trapped charges in the device. However, a coexisting relationship of resistance and capacitance was observed too, where the ligands and the gold nanoparticle dispersion played an important part in the baseline resistance of the system. This was due to the nanoparticle dispersion and the electrode contact- varying which demonstrated a change in the baseline resistance, while the capacitance remained comparable. The retention and the ON/OFF ratio were also investigated for the devices, demonstrating the need for further isolation of the nanoparticles in the devices
Analysis of a microwave patch antenna array for reflection measurements
Get PDFMicrostrip antennas and arrays are widely used antenna technology in the frequency range of 1 GHz to 100 GHz. Microstrip antennas are simple and compact, and with current printed circuit technologies they are easy to manufacture. They are used in various applications such as; satellite communications, biomedical, mobile phone technology, radar, wireless local area networks and many other applications. This research focuses on developing a microstrip antenna to be used in an array that operates in a dual-band frequency range. The long term aim of this research is to develop an antenna array which can be used for the application of breast cancer detection.
Two dual-band antenna elements are developed for this research and the antenna elements are arranged in a 2Ă2 array. Each antenna array has been designed and manufactured on a Rogers 4003 substrate. The design of the antenna elements were such that it operated in the frequency range of 5 GHz to 7 GHz creating an effect of wideband frequency operation. Four resonant frequencies were used in the range 5-7 GHz.
The antenna elements were designed and simulated using the ANSYS HFSS software platform. Five antenna arrays were tested experimentally. The initial work is to study the reflections from an object and the phase information of the reflection is analysed. A simulation model of the reflection analysis is conducted and a metal object is used for this purpose to get better understanding of the behaviour of antenna elements in an array and how effectively the phase information can be extracted to find the reflecting bodyâs nature. The antenna elements built and tested match the simulation results well.
The phase of transmitted signals has been measured experimentally and the results obtained were similar to the simulations and theory. The electric field information from the simulation has also been studied. This analysis provides a better understanding of how the reflected signals are received at the receiver antenna and it is expected that in future this method of analysis can be implemented for complex object identification
Electrical Bistability by Creating an Internal Electrical Field and Its Application in Emerging Two-terminal Electronic Memory Devices
Get PDFThis chapter focusses on the electrical bistability observed in nanocomposite memory devices that have been studied over two decades. Bistability, in the context of memory devices, has been discussed and visual tools have been employed for its examination as a general mathematical function. The bistability observed in memory devices, in terms of electrical hysteresis, has been focussed and typical curves observed in several studies over the last fifty years have been consolidated and systematically examined. The development of the field has led to much confusion in terms of understanding of the device switching mechanism, which has been investigated in detail. The discrepancies in the proposed device behaviour and the observations have over time led to the rise of many opinions/models to explain the physics of the device conduction switching. In this chapter, the charge-trap models have been examined and solutions to some open questions have been proposed in terms of analysing at the system from the perspective of field generation, instead of the material interaction
Storing Electronic information on Semi-Metal Nanoparticles
Get PDFThe file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. Open Access article.This paper presents the use of selenium nanoparticles for the application of information storage in two terminal electronic memory devices. Selenium is a semi-metal with interesting electronic and optical
properties that have seldom been studied in terms of electronic memory. In this study selenium
nanoparticles have been demonstrated as an embedded charge storage layer between silicon oxide
tunnel layer and silicon nitride blocking layer. The electrical characterisation demonstrates clear
evidence that charge storage is taking place, and that it is indispensable without the presence of
nanoparticles. AFM images show that selenium nanoparticles are almost uniformly distributed on
Silicon substrate having a thin silicon dioxide tunnelling layer, and the electrical retention
measurement shows potential for long term data storag
Efficacy of vaginal dilator use in preventing vaginal stenosis among cervical and endometrial cancer patients underwent radiotherapy
Get PDFBackground: Vaginal dilators (VD) are effective in the prevention of vaginal stenosis in patients undergoing pelvic radiotherapy for gynaecological malignancies. This study was aimed to assess the efficacy of VD use in preventing post radiotherapy vaginal stenosis in cervical and endometrial cancer patients.Methods: A cohort study was designed among patients (20-70 years) with biopsy proven endometrial and cervical carcinoma who underwent pelvic radiotherapy were included. Patients with cervical carcinoma (FIGO stage-IA to IVA), endometrial carcinoma (FIGO stage IB grade III, FIGO stage II), histology of squamous cell carcinoma, adenocarcinoma and performance score-ECOG 1 were included in the study. Assessment included clinical history, general examination, pelvic examination at 3 monthly intervals till 1 year. Grading of vaginal stenosis was assessed using LENT SOMA grading system.Results: A total of 42 patients with 20 patients using vaginal dilators and 22 patients who refused to use VD were assigned. It was effective for 60% of VD users compared to 20% of nonusers (p=0.007) at 9 months follow up. While at 12 months follow up, it was effective for 58% of VD users compared to 16.6% of nonusers (p=0.066). Percent adherence was maximum in the 1st and 2ndquarter and declined to 61% by the 4th quarter. The total adherence was 97%.Conclusions: There was 55% vs 22.7% effectiveness to prevent the vaginal stenosis among VD users. All patients need proper counselling, motivation and support for regular usage of VD which will ultimately help in reducing the incidence of vaginal stenosis
Electrochemical energy storing performances of printed LaFeO3 coated with PEDOT: PSS for hybrid supercapacitors
Get PDFeveloping advanced smart energy storage devices demanded new functional materials to store energy effectively and deliver power quickly. In this work, we studied the energy-storing performance of perovskite material, lanthanum ferrite (LaFeO3), prepared by the solid-state reaction method. The screen-printed LaFeO3 and graphite electrodes are used to develop hybrid supercapacitors (HSCs) with KOH electrolyte. Varying the sintering temperature of the LaFeO3 perovskite electrode (800 °C, 900 °C, and 1000 °C) leads to changes in the surface and crystalline properties, which impact the electrochemical properties and overall energy-storing performance of the HSC. The surface of the LaFeO3 electrode is modified with organic conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), which enhances the energy storage of the HSC. The developed HSC based on LaFeO3, sintered at 1000 °C and surface modified with PEDOT: PSS, exhibited a specific capacitance of 12.007 mFâcmâ2 at a current density of 0.075 mAâcmâ2. This value is two times higher than (5.874 mFâcmâ2) without the surface modification of LaFeO3 at 1000 °C. This study provides valuable insights into the electrochemical performances of the ABO3 perovskite (LaFeO3) electrodes for the next generation of portable energy storage devices
Smart-Textile-Based Electrochemical Capacitive Ionic Sensors for High-Performance Epidermal Electronics
Get PDFRecently, biomedical engineering has placed greater importance on wearable and disposable health-care monitoring devices. Various degradable biosensors have been developed to measure human parameters, such as temperature, pH, pressure, strain, and ion concentration, utilizing bodily fluids, such as sweat, for analysis. In this letter, we developed a new textile-based electrochemical capacitive sensor (TECS) employing multiwalled carbon nanotube-coated cellulose cloth. The electrodes for the TECS were fabricated using a drop coating method, and their surface morphology was evaluated by scanning electron microscopic images. Cyclic voltammetry analysis of the TECS revealed that the fabricated sensor exhibited a sensitivity of 0.29 ”A/log [Na + ] in the concentration range of 0â16 mM NaCl. The device operates on an electrochemical capacitive mechanism, exhibiting a specific capacitance variation of 6.9 ”Fâ
cm â2 across the NaCl concentration range of 0â16 mM. The electrochemical impedance spectroscopic analysis in the frequency range of 10 mHz to 1 MHz indicates the impact of ionic concentration variation, particularly in the low-frequency range. The fabricated TECS offers high sensing performance, biodegradability, and disposability, attributed to its development on cellulose cloth. The developed sensor has potential application in epidermal electronics through integration with smart textiles and offers significant opportunities in wearable biomedical devices
