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Research Work:

Additive Manufacturing/ 3D Printing of Chalcogenide Glass: We have developed and implemented a process flow to obtain chalcogenide glass nanoparticle ink from 5N pure elements. With the produced ink, using a Dimatix inkjet printer, we have successfully printed thin films of chalcogenide glass. Currently we are working to optimize the sintering process.                                                   Printed Chalcogenide Glass Thin Film (Scale 100 micron)

Optical Properties of Phase Change Chalcogenide Glasses: We are currently working to correlate change in optical properties in evaporated chalcogenide glass thin films with thermally induced phase change. This also involves implementing a setup in future to analyze the thermo-optical properties of chalcogenide glass thin films.

Research on glass formation of semiconducting glasses: prediction of the glass formation in new chalcogenide and chalco-halide systems based on the Constraint counting theory and chemical bonding in the glasses and synthesis of the glasses. The new glasses have been obtained due to chemical modification mainly by metals and halogens. Approaches have been persuaded to develop understanding of the nature of the chemical and mechanical thresholds in these glasses. The proper characterization of the glassy materials and their structure have been achieved using DSC, MDSC, electron microscopy, X-ray scattering, Raman scattering, Mössbauer spectroscopy and density measurements.

Formation of microstructures on thin films: using the intrinsic photosensitivity of the chalcogenide glasses and photodiffusion of silver in them. The diffusion kinetics is optimized by application of bilayered structures or chemically modified silver containing glasses. The structures are being formed due to selective chemical etching of the illuminated and non-illuminated parts of the films. The kinetic of the chemical dissolution process has been investigated and optimized due to application of particular processing of the films involving selective dissolving solutions or surface-active substances. Designing of ovonic electronic memory devices.

Real time optical recording on thin chalcogenide films: The research is focused into two areas: obtaining of an image due to phase change (photocrystallization of the films) or by modification of the polymer network leading to change in the optical properties of the films and hence to formation of an image. In this way optical elements for the IR optics as well as holographic gratings have been produced on thin films. This technology may be also applied for creation of optical elements on fibers, prepared by these glasses, so avoiding the coupling losses in them. Application of the gratings in mechanical strengths studies and opto-electronic neural networks has been experimented and optimized on hand of the chemical composition of the glasses and the recording conditions. Attempts have been made to understand all the photoinduced effects in the view of the defects existing in the amorphous chalcogenide matrix.

Image of an opto-electronic neural network

Programmable metallization cell ( PMC) memory devices:  These devices are based on formation of solid solution in a thin film of chacogenide glass due to diffusion of Ag into the chalcogenide matrix. If electrodes are formed in contact with a layer of the solid solution, an anode, which has oxidizable Ag and an inert cathode, and a voltage is applied between them, the positively charged metal ions will migrate toward the cathode region. At small applied bias (less tan 1V) in structures, which are commensurate with state-of-the-art integrated device geometries, the ions will come out of solution at the cathode to rapidly form a stable metallic electrodeposit, which may be made to extend from the cathode to the anode. This low resistance electrodeposit acts to short-out the relatively high resistance glass and hence the overall resistance of the structure can be reduced by many orders of magnitude via this non-volatile electrically-stimulated deposition process. A reverse bias will cause electrodissolution of the metal link, returning the device to a high resistance state (view the I-V characteristic and the R-V characteristic PowerPoint Presentations) and this write-erase cycle may be repeated many times (view the Retention PowerPoint Presentation).  These devices are highly scalable – up to now 40 nm devices have been created but smaller are possible as well.

image of Schematic presentation of the high resistive and low resistive condition of a memristive nanoionic electrochemical device
Schematic presentation of the high resistive and low resistive condition of a memristive nanoionic electrochemical device.

Resonant frequency alteration: In-situ frequency control of high Q microelectromechanical resonators is desirable as it is difficult to make structures that have an accurately defined and maintainable resonant frequency due to nanoscale material/processing irregularities and environmental factors (oxidation, condensation, etc.).  We have demonstrated a tunable MEMS resonator using our PMC electrolyte-electrodeposit system, (view the MEMS Schematic PowerPoint Presentation).  The resonator testbed is actually a set of 1 mm thick suspended polycrystalline silicon beams, ranging from 50 to 200 mm in length, with an 80 nm thick film of Ag-Ge-Se (sub-saturated) electrolyte on their top surface.  A silver electrode is formed at one end and both ends have aluminum pads added to facilitate bonding/packaging for electrical characterization.  The electrodeposit is made to form on the beam to change both its vibrating mass and stiffness.

Diagram that represents Resonant frequency Alteration
Formation of elements for bio-lab on a chip: developing of materials for valves in microchannel systems and cantilevers for bio-labs on a chip based on chalcogenide glasses with PMC electrochemically grown silver pathways.

Diagram showing Formation of elements for bio-lab on a chipImage of Solid Electroyte and Silver Electrodeposit

Alteration of reflectance: Surface electrodeposition can be used to alter the reflectance of a surface as the optical properties of the metal are obviously radically different from those of the electrolyte film.  To demonstrate this, we created solid electrolyte (50 nm thick Ag-Ge-Se) patterns on thick oxide grown on silicon wafers, with wide electrodes at either end (Ag and Ni).  Before the application of a bias, the light is able to pass through the thin film to be reflected by the substrate with little impediment, as shown in this Optical PowerPoint Presentation (ppt).

Image of a Clear Pixel   Image of an Occluded Pixel

Chalcogenide Glass Radiation Sensor: We are developing a low cost, high performance microelectronic device that reacts to  x-ray or gamma radiation to produce an easily measured change in electrical resistance. This radiation sensor is a two-terminal micro device with an active region consisting of a chalcogenide glass (as shown in this Radiation Sensor PowerPoint Presentation).  Exposure to ionizing radiation stimulates radiation induced effects (RIE) in the active region which promotes silver (Ag) diffusion and incorporation in the ChG thereby reducing the material’s resistivity. Since these devices are based on amorphous films, they can be fabricated on flexible and non-planar substrates which will increase their range of application. This approach is characterized by completely new principles of operation that offer low power consumption, compatibility with integrated circuit fabrication, and operational reversibility which allows for calibration and reuse. Since the family of the chalcogenide glasses includes a large number of materials, there are extended possibilities to tailor the sensitivity of the sensor to particular use situations.

Fig. 12 Schematic presentation of the radiation sensorSchematic presentation of the radiation sensor

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Research Equipment

High_Temperature_Furnace

High Temperature Furnace

Vacuum Furnace

Vacuum Furnace

High Vacuum Evaporation System

High Vacuum Evaporation System

Device Characterization Probe Station

Device Characterization Probe Station

High Resolution Microscope

High Resolution Microscope

Semiconductor Parameter Analyzer HP 4155B

Semiconductor Parameter Analyzer HP 4155B

High Energy Ball Mill

High Energy Ball Mill

Temperature controlled ellipsometer stage

Temperature controlled ellipsometer stage

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