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- All Subjects: Materials Science
Description
Programmable metallization cell (PMC) technology is based on an electrochemical phenomenon in which a metallic electrodeposit can be grown or dissolved between two electrodes depending on the voltage applied between them. Devices based on this phenomenon exhibit a unique, self-healing property, as a broken metallic structure can be healed by applying an appropriate voltage between the two broken ends. This work explores methods of fabricating interconnects and switches based on PMC technology on flexible substrates. The objective was the evaluation of the feasibility of using this technology in flexible electronics applications in which reliability is a primary concern. The re-healable property of the interconnect is characterized for the silver doped germanium selenide (Ag-Ge-Se) solid electrolyte system. This property was evaluated by measuring the resistances of the healed interconnect structures and comparing these to the resistances of the unbroken structures. The reliability of the interconnects in both unbroken and healed states is studied by investigating the resistances of the structures to DC voltages, AC voltages and different temperatures as a function of time. This work also explores replacing silver with copper for these interconnects to enhance their reliability. A model for PMC-based switches on flexible substrates is proposed and compared to the observed device behavior with the objective of developing a formal design methodology for these devices. The switches were subjected to voltage sweeps and their resistance was investigated as a function of sweep voltage. The resistance of the switches as a function of voltage pulse magnitude when placed in series with a resistance was also investigated. A model was then developed to explain the behavior of these devices. All observations were based on statistical measurements to account for random errors. The results of this work demonstrate that solid electrolyte based interconnects display self-healing capability, which depends on the applied healing voltage and the current limit. However, they fail at lower current densities than metal interconnects due to an ion-drift induced failure mechanism. The results on the PMC based switches demonstrate that a model comprising a Schottky diode in parallel with a variable resistor predicts the behavior of the device.
ContributorsBaliga, Sunil Ravindranath (Author) / Kozicki, Michael N (Thesis advisor) / Schroder, Dieter K. (Committee member) / Chae, Junseok (Committee member) / Alford, Terry L. (Committee member) / Arizona State University (Publisher)
Created2011
Description
This work investigates the effects of ionizing radiation and displacement damage on the retention of state, DC programming, and neuromorphic pulsed programming of Ag-Ge30Se70 conductive bridging random access memory (CBRAM) devices. The results show that CBRAM devices are susceptible to both environments. An observable degradation in electrical response due to total ionizing dose (TID) is shown during neuromorphic pulsed programming at TID below 1 Mrad using Cobalt-60. DC cycling in a 14 MeV neutron environment showed a collapse of the high resistance state (HRS) and low resistance state (LRS) programming window after a fluence of 4.9x10^{12} n/cm^2, demonstrating the CBRAM can fail in a displacement damage environment. Heavy ion exposure during retention testing and DC cycling, showed that failures to programming occurred at approximately the same threshold, indicating that the failure mechanism for the two types of tests may be the same. The dose received due to ionizing electronic interactions and non-ionizing kinetic interactions, was calculated for each ion species at the fluence of failure. TID values appear to be the most correlated, indicating that TID effects may be the dominate failure mechanism in a combined environment, though it is currently unclear as to how the displacement damage also contributes to the response. An analysis of material effects due to TID has indicated that radiation damage can limit the migration of Ag+ ions. The reduction in ion current density can explain several of the effects observed in CBRAM while in the LRS.
ContributorsTaggart, Jennifer L (Author) / Barnaby, Hugh J (Thesis advisor) / Kozicki, Michael N (Committee member) / Holbert, Keith E. (Committee member) / Yu, Shimeng (Committee member) / Arizona State University (Publisher)
Created2018
Description
Programmable Metallization Cell (PMC) is a resistance-switching device based on migration of nanoscale quantities of cations in a solid electrolyte and formation of a conducting electrodeposit by the reductions of these cations. This dissertation presents electrical characterization results on Cu-SiO2 based PMC devices, which due to the na- ture of materials can be easily integrated into the current Complimentary metal oxide semiconductor (CMOS) process line. Device structures representing individual mem- ory cells based on W bottom electrode and n-type Si bottom electrode were fabricated for characterization. For the W bottom electrode based devices, switching was ob- served for voltages in the range of 500mV and current value as low as 100 nA showing the electrochemical nature and low power potential. The ON state showed a direct de- pendence on the programming current, showing the possibility of multi-bit storage in a single cell. Room temperature retention was demonstrated in excess of 105 seconds and endurance to approximately 107 cycles. Switching was observed for microsecond duration 3 V amplitude pulses. Material characterization results from Raman, X-ray diffraction, Rutherford backscattering and Secondary-ion mass spectroscopy analysis shows the influence of processing conditions on the Cu concentration within the film and also the presence of Cu as free atoms. The results seemed to indicate stress-induced void formation in the SiO2 matrix as the driving mechanism for Cu diffusion into the SiO2 film. Cu/SiO2
Si based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode.
Si based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode.
ContributorsPuthenthermadam, Sarath (Author) / Kozicki, Michael N (Thesis advisor) / Diaz, Rodolfo (Committee member) / Schroder, Dieter K. (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2011
Description
Programmable Metallization Cell (PMC) devices are, in essence, redox-based
solid-state resistive switching devices that rely on ion transport through a solid electrolyte (SE) layer from anode to cathode. Analysis and modeling of the effect of different fabrication and processing parameter/conditions on PMC devices are crucial for future electronics. Furthermore, this work is even more significant for devices utilizing back-end- of-line (BEOL) compatible materials such as Cu, W, their oxides and SiOx as these devices offer cost effectiveness thanks to their inherent foundry-ready nature. In this dissertation, effect of annealing conditions and cathode material on the performance of Cu-SiOx vertical devices is investigated which shows that W-based devices have much lower forming voltage and initial resistance values. Also, higher annealing temperatures first lead to an increase in forming voltage from 400 °C to 500 °C, then a drastic decrease at 550 °C due to Cu island formation at the Cu/SiOx interface. Next, the characterization and modeling of the bilayer Cu2O/Cu-WO3 obtained by annealing the deposited Cu/WO3 stacks in air at BEOL-compatible temperatures is presented that display unique characteristics for lateral PMC devices. First, thin film oxidation kinetics of Cu is studied which show a parabolic relationship with annealing time and an activation energy of 0.70 eV. Grown Cu2O shows a cauliflower-like morphology where feature size on the surface increase with annealing time and temperature. Then, diffusion kinetics of Cu in WO3 is examined where the activation energy of diffusion of Cu into WO3 is calculated to be 0.74 eV. Cu was found to form clusters in the WO3 host which was revealed by imaging. Moreover, using the oxidation and diffusion analyses, a Matlab model is established for modeling the bilayer for process and annealing-condition optimization. The model is built to produce the resulting Cu2O thickness and Cu concentration in Cu-WO3. Additionally, material characterization, preliminary electrical results along with modeling of lateral PMC devices utilizing the bilayer is also demonstrated. By tuning the process parameters such as deposited Cu thickness and annealing conditions, a low-resistive Cu2O layer was achieved which dramatically enhanced the electrodeposition growth rate for lateral PMC devices.
solid-state resistive switching devices that rely on ion transport through a solid electrolyte (SE) layer from anode to cathode. Analysis and modeling of the effect of different fabrication and processing parameter/conditions on PMC devices are crucial for future electronics. Furthermore, this work is even more significant for devices utilizing back-end- of-line (BEOL) compatible materials such as Cu, W, their oxides and SiOx as these devices offer cost effectiveness thanks to their inherent foundry-ready nature. In this dissertation, effect of annealing conditions and cathode material on the performance of Cu-SiOx vertical devices is investigated which shows that W-based devices have much lower forming voltage and initial resistance values. Also, higher annealing temperatures first lead to an increase in forming voltage from 400 °C to 500 °C, then a drastic decrease at 550 °C due to Cu island formation at the Cu/SiOx interface. Next, the characterization and modeling of the bilayer Cu2O/Cu-WO3 obtained by annealing the deposited Cu/WO3 stacks in air at BEOL-compatible temperatures is presented that display unique characteristics for lateral PMC devices. First, thin film oxidation kinetics of Cu is studied which show a parabolic relationship with annealing time and an activation energy of 0.70 eV. Grown Cu2O shows a cauliflower-like morphology where feature size on the surface increase with annealing time and temperature. Then, diffusion kinetics of Cu in WO3 is examined where the activation energy of diffusion of Cu into WO3 is calculated to be 0.74 eV. Cu was found to form clusters in the WO3 host which was revealed by imaging. Moreover, using the oxidation and diffusion analyses, a Matlab model is established for modeling the bilayer for process and annealing-condition optimization. The model is built to produce the resulting Cu2O thickness and Cu concentration in Cu-WO3. Additionally, material characterization, preliminary electrical results along with modeling of lateral PMC devices utilizing the bilayer is also demonstrated. By tuning the process parameters such as deposited Cu thickness and annealing conditions, a low-resistive Cu2O layer was achieved which dramatically enhanced the electrodeposition growth rate for lateral PMC devices.
ContributorsBalaban, Mehmet Bugra (Author) / Kozicki, Michael N (Thesis advisor) / Barnaby, Hugh J (Committee member) / Goryll, Michael (Committee member, Committee member) / Arizona State University (Publisher)
Created2020
Description
Over the past few years, research into the use of doped diamond in electronics has seen an exponential growth. In the course of finding ways to reduce the contact resistivity, nanocarbon materials have been an interesting focus. In this work, the transfer length method (TLM) was used to investigate Ohmic contact properties using the tri-layer stack Ti/Pt/Au on nitrogen-doped n-type conducting nano-carbon (nanoC) layers grown on (100) diamond substrates. The nanocarbon material was characterized using Secondary Ion Mass Spectrometry (SIMS), Scanning electron Microscopy (SEM) X-ray diffraction (XRD), Raman scattering and Hall effect measurements to probe the materials characteristics. Room temperature electrical measurements were taken, and samples were annealed to observe changes in electrical conductivity. Low specific contact resistivity values of 8 x 10^-5 Ωcm^2 were achieved, which was almost two orders of magnitude lower than previously reported values. The results were attributed to the increased nitrogen incorporation, and the presence of electrically active defects which leads to an increase in conduction in the nanocarbon. Further a study of light phosphorus doped layers using similar methods with Ti/Pt/Au contacts again yielded a low contact resistivity of about 9.88 x 10^-2 Ωcm^2 which is an interesting prospect among lightly doped diamond films for applications in devices such as transistors. In addition, for the first time, hafnium was substituted for Ti in the contact stack (Hf/Pt/Au) and studied on nitrogen doped nanocarbon films, which resulted in low contact resistivity values on the order of 10^-2 Ωcm^2. The implications of the results were discussed, and recommendations for improving the experimental process was outlined. Lastly, a method for the selective area growth of nanocarbon was developed and studied and the results provided an insight into how different characterizations can be used to confirm the presence of the nanocrystalline diamond material, the limitations due to the film thickness was explored and ideas for future work was proposed.
ContributorsAmonoo, Evangeline Abena (Author) / Thornton, Trevor (Thesis advisor) / Alford, Terry L (Thesis advisor) / Anwar, Shahriar (Committee member) / Theodore, David (Committee member) / Arizona State University (Publisher)
Created2023