Optical controlled graphene-based nonvolatile ternary-logic transistor with azobenzene copolymer ... more Optical controlled graphene-based nonvolatile ternary-logic transistor with azobenzene copolymer Appl. Phys. Lett. 102, 013505 (2013) Note: A very simple circuit for piezo actuator pseudo-tracking for continuous-wave cavity ring-down spectroscopy Rev. Sci. Instrum. 84, 016102 A distributed, graphical user interface based, computer control system for atomic physics experiments Rev. Sci. Instrum. 84, 015105 (2013) High performance CMOS-like inverter based on an ambipolar organic semiconductor and low cost metals AIP Advances 3, 012101 Bipolar snapback in junctionless transistors for capacitorless dynamic random access memory
ABSTRACT Miniature high-resolution sensors are required in integrated systems. In the field of hi... more ABSTRACT Miniature high-resolution sensors are required in integrated systems. In the field of high resolution sensors, available sensors can be separated into two categories: small size sensor but having a limited range and high range sensor but with prohibitive size. This paper describes a long-range miniature position sensor. We propose to use two optical probes (1 mm diameter, 15 mm length for each) in front of a silicon grating (size : 20 times 20 mm2 ; thickness < 1 mm ; teeth length : 653 mum ; teeth height : 96 mum) in order to measure on a millimetric range with a submicrometric resolution. First, the principle of the sensor is given. Then, the grating sizing method is described with the best limit of resolution as the main criterion. After that, the silicon grating fabrication is explained : it was fabricated by photolithography and anisotropic wet etching solution (KOH:H2O). Measures on a 2.9 mm range with a quasi-linear sensitivity of (0.92 plusmn 0.01) mV/mum are obtained. On this range, the limit of resolution is 163 nm rms.
ABSTRACT Metal-insulator-metal (MIM) devices based on titanium dioxide thin films exhibit resisti... more ABSTRACT Metal-insulator-metal (MIM) devices based on titanium dioxide thin films exhibit resistive switching behaviour (RS) i.e. they have the ability to switch the electrical resistance between high-resistive states (HRS) and low-resistive states (LRS) by application of an appropriate voltage. This behaviour makes titanium dioxide thin films extremely valuable for memory applications. The physical mechanism behind RS remains a controversial subject but has been suggested that it could be interface-type, without accompanying structural changes of the oxide, or filament-type with formation of reduced titanium oxide phases in the film. In this work, X-ray absorption spectroscopy (XAS) at the Ti K-edge (4966 eV) was used to characterize the atomic-scale structure of a non-stoichiometric TiO2-x thin film before and after annealing and for the first time after inclusion in a MIM device based on a Cr/Pt/TiO2-x/Pt stack developed on an oxidised silicon wafer. The advantage of the XAS technique is that is element-specific. Therefore, by tuning the energy to the Ti K-edge absorption, contributions from the Pt, Cr and Si in the stack are eliminated. In order to investigate the structure of the film after electrical switching, XAS analysis at the Ti K-edge was again performed for the first time on the Cr/Pt/TiO2-x/Pt stack in its virgin state and after switching to LRS by application of an appropriate bias. X-ray absorption near-edge structure (XANES) was employed to assess local coordination and oxidation state of the Ti and X-ray absorption fine structure (EXAFS) was used to assess bond distances, coordination numbers and Debye-Waller factors. XAS analysis revealed that the as-deposited film is amorphous with a distorted local octahedral arrangement around Ti (average Ti-O distance of 1.95 ? and coordination number of 5.2) and has a majority oxidation state of Ti+4 with a slight content of Ti+3. The film remains amorphous upon insertion into the stack structure and after electrical switching but crystallizes as anatase upon annealing at 600?C. These results do not give any indication of the appearance of conducting filaments upon switching and are more compatible with homogeneous interface mechanisms.
2013 IEEE International Symposium on Circuits and Systems (ISCAS2013), 2013
Short-term synaptic plasticity (STP) is a mechanism identified in brain systems according to whic... more Short-term synaptic plasticity (STP) is a mechanism identified in brain systems according to which the effective connection strength (synaptic strength) between two neurons varies dynamically with recent communication history. As a consequence, the amplitude of the post-synaptic potential in response to a single pre-synaptic event, so-called "spike", may increase (short-term facilitation) or decrease (short-term depression) with consecutive presynaptic stimulation. However, in contrast to Long-term Synaptic plasticity, these changes are temporary and are typically restored in the absence of input. Interestingly, however, a single neuron which receives input via both facilitating and depressing synapses has improved discrimination capability, distinguishing, for instance, between a sequence of events and a sequence of the same events presented in the reversed order. We, therefore, studied the memory mechanisms in emerging non-CMOS devices with a view to application in temporal pattern recognition and detection, inspired by the STP mechanisms. In particular, we demonstrate that memristors can exhibit a resembling behavior to STP due to an inherent volatility and hysteresis. When stimulated by closely spaced pulse waves, the conductance of the device decreases similar to what a depressing synapse would do if presented with consecutive pre-synaptic spikes. This work paves the way for employing memristors in solving spatio-temporal sequence learning problems.
2014 IEEE International Symposium on Circuits and Systems (ISCAS), 2014
ABSTRACT We demonstrate a practical application of memristors in a cross-bar memory array. The fu... more ABSTRACT We demonstrate a practical application of memristors in a cross-bar memory array. The full set-up consists of only a PC, an mBED microcontroller and a PCB hosting external components and the memristor cross-bar chip. The system can be used for general purpose memory storage, but in this case we use it as a binary image storage device. A MATLAB interface allows the user to load a binary image into the memory and observe the resulting internal memory states of each memristor in the array along with key performance metrics describing the speed and degree of success of the memory 'write' operation.
2014 IEEE International Symposium on Circuits and Systems (ISCAS), 2014
ABSTRACT Accurate modeling of memristive devices is a critical condition that will allow the real... more ABSTRACT Accurate modeling of memristive devices is a critical condition that will allow the realization of large-scale memristor based circuits. The current methodology regarding modeling focuses on obtaining realistic pinched hysteresis curves, which are memristor signatures, but these do not hold useful information regarding device performance. We divert from this practice and propose a SPICE memristor model constructed based on qualitative verified assumptions of real memristive device operation. Our model introduces volatile effects that render a rate-dependent operation, and also accounts for both bipolar and unipolar switching. We demonstrate its plausibility via a wealth of simulation cases, which are qualitatively similar to several memristor dynamics reported in literature. Finally our model is benchmarked against measured results acquired by solid-state TiO2 memristors.
2014 IEEE International Symposium on Circuits and Systems (ISCAS), 2014
ABSTRACT Event-based computation is a well-established way of reducing the complexity of neural m... more ABSTRACT Event-based computation is a well-established way of reducing the complexity of neural modelling, often used as an enabling step towards the simulation of large neuronal ensembles. Recently, the advent of the physical memristor has provided the scientific community with a stand-alone nanoelectronic device that exhibits strongly 'synapse-like' behaviour and can be used in general neural modelling. In this paper we review the suitability of the most common, basic memristor models for use in tandem with event-based techniques and conclude that neither of them can support spike timing-dependent plasticity (STDP); a staple of modern neuroscience.We then identify the necessary attributes of any model that can enmesh STDP into event-based computation and present measured results evidencing that solid-state TiO2-based memristors intrinsically support such feature.
This work exploits the coexistence of both resistance and capacitance memory effects in TiO 2 -ba... more This work exploits the coexistence of both resistance and capacitance memory effects in TiO 2 -based two-terminal cells. Our Pt/TiO 2 /TiO x /Pt devices exhibit an interesting combination of hysteresis and non-zero crossing in their current-voltage (I-V) characteristic that indicates the presence of capacitive states. Our experimental results demonstrate that both resistance and capacitance states can be simultaneously set via either voltage cycling and/or voltage pulses. We argue that these state modulations occur due to bias-induced reduction of the TiO x active layer via the displacement of ionic species.
In this work, we show that identical TiO 2 -based memristive devices that possess the same initia... more In this work, we show that identical TiO 2 -based memristive devices that possess the same initial resistive states are only phenomenologically similar as their internal structures may vary significantly, which could render quite dissimilar switching dynamics. We experimentally demonstrated that the resistive switching of practical devices with similar initial states could occur at different programming stimuli cycles. We argue that similar memory states can be transcribed via numerous distinct active core states through the dissimilar reduced TiO 2-x filamentary distributions. Our hypothesis was finally verified via simulated results of the memory state evolution, by taking into account dissimilar initial filamentary distribution.
2014 IEEE International Symposium on Circuits and Systems (ISCAS), 2014
ABSTRACT In this paper we present a practical approach to employ solid-state TiO2 memristors as t... more ABSTRACT In this paper we present a practical approach to employ solid-state TiO2 memristors as tunable loads in filter configurations. First, memristive devices are employed in discrete realizations of tunable active filter topologies. Using an external programming circuit to set the devices to a desired memristive state enables control of the filter's characteristics, namely passband boundaries and quality factor. Utilization of a memristor as a tunable load in low-pass and band-pass filter topologies is then experimentally demonstrated. We further expand this concept by demonstrating an amplitude-controlled gain amplifier topology. In this topology, instead of using external control circuitry to set the memristive state, the state is set internally during operation, providing an automatic gain control.
Large attention has recently been given to a novel technology named memristor, for having the pot... more Large attention has recently been given to a novel technology named memristor, for having the potential of becoming the new electronic device standard. Yet, its manifestation as the fourth missing element is rather controversial among scientists. Here we demonstrate that TiO 2 -based metal-insulator-metal devices are more than just a memory-resistor. They possess resistive, capacitive and inductive components that can concurrently be programmed; essentially exhibiting a convolution of memristive, memcapacitive and meminductive effects. We show how non-zero crossing current-voltage hysteresis loops can appear and we experimentally demonstrate their frequency response as memcapacitive and meminductive effects become dominant.
A fiber optic sensor for two-dimension linear displacement measurements is described. This sensor... more A fiber optic sensor for two-dimension linear displacement measurements is described. This sensor can have resolution and range in nanometer and millimeter scales, respectively. After validation of the sensor principle in one dimension, the displacement methods in two dimensions are described and the experimental measurements are realized by the use of the sensor and high precision actuators. The best and
ABSTRACT We demonstrate that indium–tin-oxide (ITO), when used as an active core material in meta... more ABSTRACT We demonstrate that indium–tin-oxide (ITO), when used as an active core material in metal–insulator–metal type devices, facilitates resistive switching. We fabricated devices both on silicon as well as quartz wafers, to demonstrate transparent devices. Furthermore, we investigated the influence of active core thickness on the devices' characteristics, showing that their switching threshold scales with the ITO thickness. Unipolar switching was observed for devices comprising thick ITO films while bipolar switching occurred for both thin and thick ITO films at the absence of high voltage forming steps. Our study demonstrates that ITO holds good potential for resistive memory applications.
ABSTRACT A novel thermal micro-stepper motor (TMM) principle based on friction and thermal expans... more ABSTRACT A novel thermal micro-stepper motor (TMM) principle based on friction and thermal expansion has been developed. Its objective is to move, rotate, align and adjust micro-objects with nanometre precision while having a long stroke. In this study, the design of a linear and a rotational motor and their microfabrication is presented. The fabricated devices were characterised and the first experimental results are presented. Several challenges in MEMS design, microfabrication and micro-assemble the future moving axel with the microsystem had to be overcome.
ABSTRACT Polycrystalline carbon tubes were generated by CVD inside electrochemically prepared nan... more ABSTRACT Polycrystalline carbon tubes were generated by CVD inside electrochemically prepared nano-porous anodic aluminium oxide membranes. This method produced nano-tubes without catalyst, featuring polycrystalline and a few layer thick walls. Individual tubes could be isolated and suspended on microfabricated substrates such that they formed single-side clamped beams. These beams were then used to investigate their mechanical properties employing electrostatic forces for bending the tubes beyond their mechanical stability where pull-in occurs, which could be detected by monitoring the current flowing from the tube to the substrate.
The design of a fibre-optic sensor able to measure high-precision angular displacements is presen... more The design of a fibre-optic sensor able to measure high-precision angular displacements is presented. The sensor has a small size which allows easy integration in miniature mechanical systems. Two configurations are designed: lens-free configuration and GRIN micro-lens configuration for which the micro-lens is fixed on the tip of the probe. The experimental results obtained by the angular displacement sensor based on the lens-free configuration are compared with the simulation results based on the modelling of the system and a good agreement is found. Then, a long-range measurement technique is described. In the 'lens-free and long-range configuration', the limit of resolution is measured (2 × 10 −3• ) or calculated (4.8 × 10 −4• ) over a range of [−23.4 • , +23.4 • ]. In the 'GRIN lens and long-range configuration', the best limit of resolution is decreased to 2.2 × 10 −4• but over a smaller range of [-14.5 • , +14.5 • ]. Finally, the sensor in its 'lens-free configuration' design is integrated into a miniature electromagnetic actuator to determine its stroke by a comparison of the output signal obtained between this unknown-stroke actuator and a rotating stage for which the stroke was precisely known.
This work exploits the switching dynamics of nanoscale resistive random access memory (ReRAM) cel... more This work exploits the switching dynamics of nanoscale resistive random access memory (ReRAM) cells with particular emphasis on the origin of the observed variability when cells are consecutively cycled/programmed at distinct memory states. It is demonstrated that this variance is a common feature of all ReRAM elements and is ascribed to the formation and rupture of conductive filaments that expand across the active core, independently of the material employed as the active switching core, the causal physical switching mechanism, the switching mode (bipolar/unipolar) or even the unit cells' dimensions. Our hypothesis is supported through both experimental and theoretical studies on TiO 2 and In 2 O 3 : SnO 2 (ITO) based ReRAM cells programmed at three distinct resistive states. Our prototypes employed TiO 2 or ITO active cores over 5 × 5 µm 2 and 100 × 100 µm 2 cell areas, with all tested devices demonstrating both unipolar and bipolar switching modalities. In the case of TiO 2 -based cells, the underlying switching mechanism is based on the non-uniform displacement of ionic species that foster the formation of conductive filaments. On the other hand, the resistive switching observed in the ITO-based devices is considered to be due to a phase change mechanism. The selected experimental parameters allowed us to demonstrate that the observed programming variance is a common feature of all ReRAM devices, proving that its origin is dependent upon randomly oriented local disorders within the active core that have a substantial impact on the overall state variance, particularly for high-resistive states.
Journal of Micro/Nanolithography, MEMS, and MOEMS, 2008
ABSTRACT Silicon gratings are fabricated using micromachining techniques. The gratings are used w... more ABSTRACT Silicon gratings are fabricated using micromachining techniques. The gratings are used with fiber optic probes to measure high-resolution and long-range linear displacements. Different parameters of the fabrication process such as the etching solution, the concentration of the etchant, and the temperature are optimized to achieve a mirror-like surface quality of the grating steps. For each parameter set, the resulting roughness and flatness are analyzed and discussed. Finally, linear displacement measurements are performed with the optimized grating as a component of a long-range fiber optic sensor. A resolution better than 34 nm and a measurement range up to 8.7 mm are obtained. c 2008 Society of Photo-Optical Instrumentation Engineers.
Optical controlled graphene-based nonvolatile ternary-logic transistor with azobenzene copolymer ... more Optical controlled graphene-based nonvolatile ternary-logic transistor with azobenzene copolymer Appl. Phys. Lett. 102, 013505 (2013) Note: A very simple circuit for piezo actuator pseudo-tracking for continuous-wave cavity ring-down spectroscopy Rev. Sci. Instrum. 84, 016102 A distributed, graphical user interface based, computer control system for atomic physics experiments Rev. Sci. Instrum. 84, 015105 (2013) High performance CMOS-like inverter based on an ambipolar organic semiconductor and low cost metals AIP Advances 3, 012101 Bipolar snapback in junctionless transistors for capacitorless dynamic random access memory
ABSTRACT Miniature high-resolution sensors are required in integrated systems. In the field of hi... more ABSTRACT Miniature high-resolution sensors are required in integrated systems. In the field of high resolution sensors, available sensors can be separated into two categories: small size sensor but having a limited range and high range sensor but with prohibitive size. This paper describes a long-range miniature position sensor. We propose to use two optical probes (1 mm diameter, 15 mm length for each) in front of a silicon grating (size : 20 times 20 mm2 ; thickness < 1 mm ; teeth length : 653 mum ; teeth height : 96 mum) in order to measure on a millimetric range with a submicrometric resolution. First, the principle of the sensor is given. Then, the grating sizing method is described with the best limit of resolution as the main criterion. After that, the silicon grating fabrication is explained : it was fabricated by photolithography and anisotropic wet etching solution (KOH:H2O). Measures on a 2.9 mm range with a quasi-linear sensitivity of (0.92 plusmn 0.01) mV/mum are obtained. On this range, the limit of resolution is 163 nm rms.
ABSTRACT Metal-insulator-metal (MIM) devices based on titanium dioxide thin films exhibit resisti... more ABSTRACT Metal-insulator-metal (MIM) devices based on titanium dioxide thin films exhibit resistive switching behaviour (RS) i.e. they have the ability to switch the electrical resistance between high-resistive states (HRS) and low-resistive states (LRS) by application of an appropriate voltage. This behaviour makes titanium dioxide thin films extremely valuable for memory applications. The physical mechanism behind RS remains a controversial subject but has been suggested that it could be interface-type, without accompanying structural changes of the oxide, or filament-type with formation of reduced titanium oxide phases in the film. In this work, X-ray absorption spectroscopy (XAS) at the Ti K-edge (4966 eV) was used to characterize the atomic-scale structure of a non-stoichiometric TiO2-x thin film before and after annealing and for the first time after inclusion in a MIM device based on a Cr/Pt/TiO2-x/Pt stack developed on an oxidised silicon wafer. The advantage of the XAS technique is that is element-specific. Therefore, by tuning the energy to the Ti K-edge absorption, contributions from the Pt, Cr and Si in the stack are eliminated. In order to investigate the structure of the film after electrical switching, XAS analysis at the Ti K-edge was again performed for the first time on the Cr/Pt/TiO2-x/Pt stack in its virgin state and after switching to LRS by application of an appropriate bias. X-ray absorption near-edge structure (XANES) was employed to assess local coordination and oxidation state of the Ti and X-ray absorption fine structure (EXAFS) was used to assess bond distances, coordination numbers and Debye-Waller factors. XAS analysis revealed that the as-deposited film is amorphous with a distorted local octahedral arrangement around Ti (average Ti-O distance of 1.95 ? and coordination number of 5.2) and has a majority oxidation state of Ti+4 with a slight content of Ti+3. The film remains amorphous upon insertion into the stack structure and after electrical switching but crystallizes as anatase upon annealing at 600?C. These results do not give any indication of the appearance of conducting filaments upon switching and are more compatible with homogeneous interface mechanisms.
2013 IEEE International Symposium on Circuits and Systems (ISCAS2013), 2013
Short-term synaptic plasticity (STP) is a mechanism identified in brain systems according to whic... more Short-term synaptic plasticity (STP) is a mechanism identified in brain systems according to which the effective connection strength (synaptic strength) between two neurons varies dynamically with recent communication history. As a consequence, the amplitude of the post-synaptic potential in response to a single pre-synaptic event, so-called "spike", may increase (short-term facilitation) or decrease (short-term depression) with consecutive presynaptic stimulation. However, in contrast to Long-term Synaptic plasticity, these changes are temporary and are typically restored in the absence of input. Interestingly, however, a single neuron which receives input via both facilitating and depressing synapses has improved discrimination capability, distinguishing, for instance, between a sequence of events and a sequence of the same events presented in the reversed order. We, therefore, studied the memory mechanisms in emerging non-CMOS devices with a view to application in temporal pattern recognition and detection, inspired by the STP mechanisms. In particular, we demonstrate that memristors can exhibit a resembling behavior to STP due to an inherent volatility and hysteresis. When stimulated by closely spaced pulse waves, the conductance of the device decreases similar to what a depressing synapse would do if presented with consecutive pre-synaptic spikes. This work paves the way for employing memristors in solving spatio-temporal sequence learning problems.
2014 IEEE International Symposium on Circuits and Systems (ISCAS), 2014
ABSTRACT We demonstrate a practical application of memristors in a cross-bar memory array. The fu... more ABSTRACT We demonstrate a practical application of memristors in a cross-bar memory array. The full set-up consists of only a PC, an mBED microcontroller and a PCB hosting external components and the memristor cross-bar chip. The system can be used for general purpose memory storage, but in this case we use it as a binary image storage device. A MATLAB interface allows the user to load a binary image into the memory and observe the resulting internal memory states of each memristor in the array along with key performance metrics describing the speed and degree of success of the memory 'write' operation.
2014 IEEE International Symposium on Circuits and Systems (ISCAS), 2014
ABSTRACT Accurate modeling of memristive devices is a critical condition that will allow the real... more ABSTRACT Accurate modeling of memristive devices is a critical condition that will allow the realization of large-scale memristor based circuits. The current methodology regarding modeling focuses on obtaining realistic pinched hysteresis curves, which are memristor signatures, but these do not hold useful information regarding device performance. We divert from this practice and propose a SPICE memristor model constructed based on qualitative verified assumptions of real memristive device operation. Our model introduces volatile effects that render a rate-dependent operation, and also accounts for both bipolar and unipolar switching. We demonstrate its plausibility via a wealth of simulation cases, which are qualitatively similar to several memristor dynamics reported in literature. Finally our model is benchmarked against measured results acquired by solid-state TiO2 memristors.
2014 IEEE International Symposium on Circuits and Systems (ISCAS), 2014
ABSTRACT Event-based computation is a well-established way of reducing the complexity of neural m... more ABSTRACT Event-based computation is a well-established way of reducing the complexity of neural modelling, often used as an enabling step towards the simulation of large neuronal ensembles. Recently, the advent of the physical memristor has provided the scientific community with a stand-alone nanoelectronic device that exhibits strongly 'synapse-like' behaviour and can be used in general neural modelling. In this paper we review the suitability of the most common, basic memristor models for use in tandem with event-based techniques and conclude that neither of them can support spike timing-dependent plasticity (STDP); a staple of modern neuroscience.We then identify the necessary attributes of any model that can enmesh STDP into event-based computation and present measured results evidencing that solid-state TiO2-based memristors intrinsically support such feature.
This work exploits the coexistence of both resistance and capacitance memory effects in TiO 2 -ba... more This work exploits the coexistence of both resistance and capacitance memory effects in TiO 2 -based two-terminal cells. Our Pt/TiO 2 /TiO x /Pt devices exhibit an interesting combination of hysteresis and non-zero crossing in their current-voltage (I-V) characteristic that indicates the presence of capacitive states. Our experimental results demonstrate that both resistance and capacitance states can be simultaneously set via either voltage cycling and/or voltage pulses. We argue that these state modulations occur due to bias-induced reduction of the TiO x active layer via the displacement of ionic species.
In this work, we show that identical TiO 2 -based memristive devices that possess the same initia... more In this work, we show that identical TiO 2 -based memristive devices that possess the same initial resistive states are only phenomenologically similar as their internal structures may vary significantly, which could render quite dissimilar switching dynamics. We experimentally demonstrated that the resistive switching of practical devices with similar initial states could occur at different programming stimuli cycles. We argue that similar memory states can be transcribed via numerous distinct active core states through the dissimilar reduced TiO 2-x filamentary distributions. Our hypothesis was finally verified via simulated results of the memory state evolution, by taking into account dissimilar initial filamentary distribution.
2014 IEEE International Symposium on Circuits and Systems (ISCAS), 2014
ABSTRACT In this paper we present a practical approach to employ solid-state TiO2 memristors as t... more ABSTRACT In this paper we present a practical approach to employ solid-state TiO2 memristors as tunable loads in filter configurations. First, memristive devices are employed in discrete realizations of tunable active filter topologies. Using an external programming circuit to set the devices to a desired memristive state enables control of the filter's characteristics, namely passband boundaries and quality factor. Utilization of a memristor as a tunable load in low-pass and band-pass filter topologies is then experimentally demonstrated. We further expand this concept by demonstrating an amplitude-controlled gain amplifier topology. In this topology, instead of using external control circuitry to set the memristive state, the state is set internally during operation, providing an automatic gain control.
Large attention has recently been given to a novel technology named memristor, for having the pot... more Large attention has recently been given to a novel technology named memristor, for having the potential of becoming the new electronic device standard. Yet, its manifestation as the fourth missing element is rather controversial among scientists. Here we demonstrate that TiO 2 -based metal-insulator-metal devices are more than just a memory-resistor. They possess resistive, capacitive and inductive components that can concurrently be programmed; essentially exhibiting a convolution of memristive, memcapacitive and meminductive effects. We show how non-zero crossing current-voltage hysteresis loops can appear and we experimentally demonstrate their frequency response as memcapacitive and meminductive effects become dominant.
A fiber optic sensor for two-dimension linear displacement measurements is described. This sensor... more A fiber optic sensor for two-dimension linear displacement measurements is described. This sensor can have resolution and range in nanometer and millimeter scales, respectively. After validation of the sensor principle in one dimension, the displacement methods in two dimensions are described and the experimental measurements are realized by the use of the sensor and high precision actuators. The best and
ABSTRACT We demonstrate that indium–tin-oxide (ITO), when used as an active core material in meta... more ABSTRACT We demonstrate that indium–tin-oxide (ITO), when used as an active core material in metal–insulator–metal type devices, facilitates resistive switching. We fabricated devices both on silicon as well as quartz wafers, to demonstrate transparent devices. Furthermore, we investigated the influence of active core thickness on the devices' characteristics, showing that their switching threshold scales with the ITO thickness. Unipolar switching was observed for devices comprising thick ITO films while bipolar switching occurred for both thin and thick ITO films at the absence of high voltage forming steps. Our study demonstrates that ITO holds good potential for resistive memory applications.
ABSTRACT A novel thermal micro-stepper motor (TMM) principle based on friction and thermal expans... more ABSTRACT A novel thermal micro-stepper motor (TMM) principle based on friction and thermal expansion has been developed. Its objective is to move, rotate, align and adjust micro-objects with nanometre precision while having a long stroke. In this study, the design of a linear and a rotational motor and their microfabrication is presented. The fabricated devices were characterised and the first experimental results are presented. Several challenges in MEMS design, microfabrication and micro-assemble the future moving axel with the microsystem had to be overcome.
ABSTRACT Polycrystalline carbon tubes were generated by CVD inside electrochemically prepared nan... more ABSTRACT Polycrystalline carbon tubes were generated by CVD inside electrochemically prepared nano-porous anodic aluminium oxide membranes. This method produced nano-tubes without catalyst, featuring polycrystalline and a few layer thick walls. Individual tubes could be isolated and suspended on microfabricated substrates such that they formed single-side clamped beams. These beams were then used to investigate their mechanical properties employing electrostatic forces for bending the tubes beyond their mechanical stability where pull-in occurs, which could be detected by monitoring the current flowing from the tube to the substrate.
The design of a fibre-optic sensor able to measure high-precision angular displacements is presen... more The design of a fibre-optic sensor able to measure high-precision angular displacements is presented. The sensor has a small size which allows easy integration in miniature mechanical systems. Two configurations are designed: lens-free configuration and GRIN micro-lens configuration for which the micro-lens is fixed on the tip of the probe. The experimental results obtained by the angular displacement sensor based on the lens-free configuration are compared with the simulation results based on the modelling of the system and a good agreement is found. Then, a long-range measurement technique is described. In the 'lens-free and long-range configuration', the limit of resolution is measured (2 × 10 −3• ) or calculated (4.8 × 10 −4• ) over a range of [−23.4 • , +23.4 • ]. In the 'GRIN lens and long-range configuration', the best limit of resolution is decreased to 2.2 × 10 −4• but over a smaller range of [-14.5 • , +14.5 • ]. Finally, the sensor in its 'lens-free configuration' design is integrated into a miniature electromagnetic actuator to determine its stroke by a comparison of the output signal obtained between this unknown-stroke actuator and a rotating stage for which the stroke was precisely known.
This work exploits the switching dynamics of nanoscale resistive random access memory (ReRAM) cel... more This work exploits the switching dynamics of nanoscale resistive random access memory (ReRAM) cells with particular emphasis on the origin of the observed variability when cells are consecutively cycled/programmed at distinct memory states. It is demonstrated that this variance is a common feature of all ReRAM elements and is ascribed to the formation and rupture of conductive filaments that expand across the active core, independently of the material employed as the active switching core, the causal physical switching mechanism, the switching mode (bipolar/unipolar) or even the unit cells' dimensions. Our hypothesis is supported through both experimental and theoretical studies on TiO 2 and In 2 O 3 : SnO 2 (ITO) based ReRAM cells programmed at three distinct resistive states. Our prototypes employed TiO 2 or ITO active cores over 5 × 5 µm 2 and 100 × 100 µm 2 cell areas, with all tested devices demonstrating both unipolar and bipolar switching modalities. In the case of TiO 2 -based cells, the underlying switching mechanism is based on the non-uniform displacement of ionic species that foster the formation of conductive filaments. On the other hand, the resistive switching observed in the ITO-based devices is considered to be due to a phase change mechanism. The selected experimental parameters allowed us to demonstrate that the observed programming variance is a common feature of all ReRAM devices, proving that its origin is dependent upon randomly oriented local disorders within the active core that have a substantial impact on the overall state variance, particularly for high-resistive states.
Journal of Micro/Nanolithography, MEMS, and MOEMS, 2008
ABSTRACT Silicon gratings are fabricated using micromachining techniques. The gratings are used w... more ABSTRACT Silicon gratings are fabricated using micromachining techniques. The gratings are used with fiber optic probes to measure high-resolution and long-range linear displacements. Different parameters of the fabrication process such as the etching solution, the concentration of the etchant, and the temperature are optimized to achieve a mirror-like surface quality of the grating steps. For each parameter set, the resulting roughness and flatness are analyzed and discussed. Finally, linear displacement measurements are performed with the optimized grating as a component of a long-range fiber optic sensor. A resolution better than 34 nm and a measurement range up to 8.7 mm are obtained. c 2008 Society of Photo-Optical Instrumentation Engineers.
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Papers by Ali Khiat