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Institut für Festkörperphysik

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Advanced process nodes for analog radiation tolerant ICs

Advanced CMOS process nodes like 28 nm and 40 nm have been introduced in commercial products several years ago. Usage of these processes for high performance digital circuits is being continuously and broadly exploited. But their applicability for analog functions of mixed-signal systems is still to be further explored. In particular this is an interesting research are for particle physics experiments, where scaled down MOS transistor features could offer advantages for radiation tolerance, which is a subject of this project.

We are looking for a candidate interested in device physics and IC design

    Objectives
  • Getting familiar with general radiation effects in MOS transistors
  • Understanding key differences between 28 nm and previous CMOS generations
  • Identifying issues and potentials of 28 nm / 40 nm in analog applications for highly ionizing radiation environments
    Approach/Methods/Tasks
  • Literature research oriented towards process details and known radiation effects
  • 2D TCAD modeling and analysis of PMOS and NMOS transistor
  • Process studies in Cadence environment based on documentation and simulations, including representative design examples
    Organizational matters
  • Begin: February 2019
  • Working place: IFE/TU Graz, Innfeldgasse 12
  • Employment as Studentische Projektmitarbeiter 20h/week (~1500 Euro/month) for at least 4 months.


Contact: Alicja Michalowska-Forsyth (alicja.michalowska@tugraz.at)

Modeling and Characterization of Semiconductor Devices at Cryogenic Temperatures

The objective of the master thesis is to investigate the behavior of semiconductor devices (resistors, MOS-transistors) in a CMOS-technology at temperatures below 20K. For this, both, simulations on a device-physics level and measurements of test devices should be performed. The simulations will be done in Synopsis TCAD using the latest models. Their results should clearly show the influence of temperature on electrical device properties like resistance, gain and bandwidth. Since semiconductor performance is usually not modeled in these regimes, advanced physical models can be implemented using a C++ API to account for effects not yet implemented in the software.

Initial device measurements and final model verification will be done using a cryostat and measurement equipment located in Villach. These measurements can be used to verify TCAD models and identify effects not yet accounted for in the setup.
Finally, SPICE models should be implemented for an analog simulator. These models will then be used to design circuits that operate at cryogenic temperatures in quantum computing applications.

The main tasks of this thesis work can be summarized as follows:

› Getting familiar with low-temperature effects in semiconductors including literature research
› Initial measurements of existing devices and identification of significant effects
› Getting familiar with TCAD simulations and proper setup
› Developing a TCAD setup that physically models relevant effects
› Verification of TCAD simulation results using measurements of real devices
› Implementation of a SPICE model that represents the device in an analog circuit

Infrastructure: Infineon provides access to the necessary software and technology information. Infineon also provides the possibility to participate on shared reticles in the targeted technologies (if time permits). Measurement costs (test structures, equipment time) are covered by Infineon.

The student is expected to be located in Villach for the duration of the thesis, however, agreements regarding working from home or Graz may be possible. Details upon the monthly salary for the student will be given by HR Infineon after a technical interview.

For further information, please contact Michael.Sieberer@infineon.com or p.hadley@tugraz.at.

Deposition and characterization of coatings by Molecular Layer Deposition

Molecular layer deposition (MLD) has gained attention in the past few years as the method-of-choice to synthesize (ultra-)thin pinhole-free organic/inorganic hybrid films, the so-called ´metalcones´.[1] MLD enables the deposition of such films with atomic level control over growth, due to its self-limiting nature. By post-processing of the metalcone layers, porous metal oxide can be obtained, paving the road for numerous applications, such as photocatalysis, (bio-)sensing, and separation membranes.
The objective of this master thesis will be to test and optimize novel combinations of inorganic and organic precursors, in order to obtain stable and well-defined metalcones, and subsequently to investigate different post-processing methods to obtain porous metal oxides. The porous metal oxides will be tested as photocatalytic materials. A Zinc containing molecule will be adopted as inorganic precursor, so to obtain porous zinc oxide (ZnO) after post-processing.[2] Different organic precursors will be chosen, to obtain zinc-based metalcone (i.e., zincone) layers with a variable length of the organic bridges, able to tune the final porosity of the derived oxide. The zincone and porous zinc oxide will be studied in terms of opto-chemical properties and crystallographic nature by means of spectroscopic ellipsometry (SE), Fourier transform infrared spectroscopy (FT-IR), and X-ray based techniques (X-ray reflectivity, XRR, and X-ray diffraction, XRD). Moreover, the photocatalytic activity will be tested with solution dye-removal.

[1]   P. Sundberg, M. Karppinen, Beilstein J. Nanotechnol. 2014, 5, 1104.
[2]   Q. Peng, B. Gong, R.M. VanGundy, G.N. Parsons, Chem. Mater. 2009, 21, 820.

 

Start: as soon as possible
Contacts:

Dr. Alberto Perrotta,
Institute of Solid State Physics, Room PH03-134
a.perrotta@tugraz.at

Assoc. Prof. Dr. Anna Maria Coclite,
Institute of Solid State Physics, Room PH03-124
anna.coclite@tugraz.atat

Porosimetry set-up and study

Porous materials have many advantages, such as large surface areas and the possibility to be loaded with additional (active) substances. The characterization of porosity and pore size in bulk materials is well-established, and robust theories can be used to determine the voids fraction. However, in order to adopt porous materials in electronic devices (e.g., bio- and gas-sensors) often thin films need to be used. The characterization of the porosity in thin films is not trivial and the conventional methods cannot be applied, because of the limited amount of material present.
Ellipsometric porosimetry[1][2] is a technique that allows the determination of porosity and pore size in thin films. Spectroscopic ellipsometry is used in order to detect the adsorption and desorption of molecules, obtaining in this way the volume and distribution of the pores.
The objective of this master thesis will be to run the first ellipsometric porosimeter at TU Graz! The assembly of the hardware and the programming of the software interface will be the first part of the thesis, completed by the determination of porosity in a variety of thin films (e.g., zinc oxide, hydrogels, hybrid polymers).
[1]   M.R. Baklanov, K.P. Mogilnikov, V.G. Polovinkin, F.N. Dultsev, J. Vac. Sci. Technol. B Microelectron. Nanom. Struct. 2000, 18, 1385.
[2]   M. Vayer, T.H. Nguyen, D. Grosso, C. Boissiere, M.A. Hillmyer, C. Sinturel, Macromolecules 2011, 44, 8892.

Start: as soon as possible
Contacts:

Dr. Alberto Perrotta,
Institute of Solid State Physics, Room PH03-134
a.perrotta@tugraz.at

Assoc. Prof. Dr. Anna Maria Coclite,
Institute of Solid State Physics, Room PH03-124
anna.coclite@tugraz.atat

Physical Interpretation of Machine Learning Results      >> mehr >>

The advent of Machine Learning methods has unlocked great potential in computational studies. In particular the exploration of surface structures, that was previously thought to be completely unfeasible, has surged in the recent years. At the same time, machine learning studies are often criticized for their lack of physical insight.

In this master project, we will investigate Bisphenol A aggregates on Ag(111). This system shows an interesting peculiarity: The molecules adsorb in two different ways. The rotational barriers between those two differ, such that one kind of molecules is immobile at room temperature, while the other remains mobile and cannot be sharply imaged in STM studies. The target of this thesis is to investigate the interface using an in-house developed machine learning algorithm and study the relative contribution of covalent, ionic, and van-der-Waals contributions, in order to provide an explanation for the difference between the two adsorption sites.

We seek: Highly motivated, self-propelled students with an interest in solid state physics and computational material science. Basic knowledge of Matlab and/or Python is recommended.


Compensation: € 440,-- Forschungsbeihilfe for 6 months.

Contact:
Oliver Hofmann email: o.hofmann@tugraz.at
Tel: 0316 873 8964 http://www.if.tugraz.at/hofmann
Or talk to the students in office PH 02 152 (2nd floor, right by the stairs)

Indexation of grazing incidence x-ray diffraction pattern       >> mehr >>

The solution of crystal structures from thin films is a contemporary problem in crystallography. A combined experimental / theoretical approach is used where the first step is a grazing incidence x-ray diffraction experiment. The diffraction patterns have to be indexed, which requires the assignment of Laue indices to individual Bragg peaks. The result of the indexation procedure is the geometry of the crystallographic unit cell in terms of lattice constants a, b, c, and the angles α , β , γ. For that purpose, a computer code has to be developed which performs an indexation procedure for grazing incidence diffraction pattern.

Central question of the master thesis:

How is it possible to index a diffraction pattern which arises from two different types of crystal lattices?


There are two avenues to answer this question:
A) Separation of two crystal lattices by neuronal networks. A large number (> several thousand) of diffraction patterns will be calculated and combined into a superposition of two crystal lattices. Neuronal networks will use these examples for for training, and then be applied to (experimentally obtained) diffraction patterns

B) indexation of a single phase by using a specular diffraction peak. Result: 3 real values and two integers besides the individual Laue Indices for each peak Boundary conditions: restricted volume, restricted lattice constants, find solutions for a reduced number of reflections, neglecting of one or more peaks which cannot be explained. In a subsequent step indexation of a single phase without using a specular diffraction peak will be performed.

Contact: Oliver Hofmann (o.hofmann@tugraz.at) / Roland Resel (roland.resel@tugraz.at)

Modelling thermal transport in organic semiconductors      >> mehr >>

Goal: Development of atomistically motivated structure-to-property relationships for heat transport in organic semiconductors – a property, that is crucial for device operation, but is still largely unexplored such that the suggested studies can have a huge impact.

Details: The ability of a material to transport heat is of considerable importance even in cases where its main application is not thermal- related. Some examples where this property plays a central role include thermoelectricity, thermal barrier coatings, phase-change memory, heat-assisted magnetic recording, and extends to the general problem of thermal management of a wide variety of de- vices.

The main objective of the master thesis is to develop structure-to-property relation- ships for thermal transport in organic semiconductors, a cutting-edge research direction with potential applications in fields as varied as microelectronics, optoelectronics, catalysis, and porous materials.

The studies will be addressed by combining molecular dynamics and electronic structure calculations. The applicants should be interested in solid state physics, should have strong motivation for computer simulations, and should be willing to develop codes and scripts.

At the end of the master thesis, the students will have expertise in computa- tional methods for modelling thermal transport, and will have practical knowledge in electronic structure calculations and molecular dynamics. These methodologies constitute a powerful tool to study the electronic, structural and thermodynamic properties of materials.

Aside of the academic profits, we offer a very friendly work environment.

Starting date: any time
Compensation: 440 € per month for 6-8 months
Contact:
Natalia Bedoya Martinez (bedoyamartinez@tugraz.at, Tel.:873-8465)
Egbert Zojer (egbert.zojer@tugraz.at; Tel.: 873-8475)

Charge Transfer at Mixed Physisorbed/Chemisorbed Interfaces      >> mehr >>

Inorganic/Organic interfaces are of great relevant to a large variety of applications, ranging from catalysis and corrosion protection to appliances such as large-area OLED-TVs. Of particular interest is the charge-transfer across the interface, which typically governs the overall performance of the system. Depending on the strength of the interaction between substrate and adsorbate, two archetypes for charge-transfer are commonly observed. For strongly interacting, chemisorbed molecules, new bonds are formed and each molecule at the surface becomes fractionally charged. Conversely, if the interaction is weak, i.e. the molecule physisorbs, some molecules acquire an integer electron while others remain neutral.

Some material combinations exhibit two distinct structures, where one is physisorbed and the other chemisorbed. Experimentally, a transition between these can be triggered – on a single molecule basis – e.g. via voltage pulses STM tips. The main objective of this thesis is to investigate how the electronic structure / charge-transfer mechanism evolves for phases where physisorbed and chemisorbed molecules coexist by using density functional theory calculations. Furthermore, the possibility of using other, more readily available impulses (such as electric fields or optical excitations) to switch between chemisorption and physisorption will be explored.

Contact:
Oliver Hofmann
Email: o.hofmann@tugraz.at
Tel: 0316 873 8465
http://www.if.tugraz.at/web.php?85

      >> mehr >>

The molecule HATCN is a strong electron acceptor that is commercially used in OLEDs to modify the property of metal substrates. Adsorbed on silver, this molecule shows unusual, fascinating physics. At low coverage, the molecule forms honeycomb patterns, which can be exploited as epitaxial growth template. When the coverage is increased, however, the first monolayer rearranges. This drastically changes the material properties, in particular the system’s work function.

At present only very little is known about the geometric and electronic structure of the rearranged, high- coverage phase. This is now at the focus of a joint efforts including the groups of Prof. Resel (TU Graz), and Prof. Fritz (University Jena), which will perform x-ray and low energy electron diffraction experiments and characterize the system via optical spectroscopy. The aim of this thesis is to provide complimentary computational insight to these experiments. Density-functional theory calculations will be performed in order to predict possible geometric structures, characterize the optical and vibrational properties, and understand the driving force that leads to the observed phase transition.

Contact:
Oliver Hofmann
Email: o.hofmann@tugraz.at
Tel: 0316 873 8465
http://www.if.tugraz.at/web.php?85

Deposition and Characterization of Dielectric Bragg Reflectors       >> mehr >>


Dielectric Bragg Reflectors (DBR) are commercially manufactured onto rigid substrates, using inorganic materials (e.g. SiO2, TiO2). Recently, organic DBR are under investigation because they allow creation of tunable optical properties. During the wet fabrication processes, the choice of polymers that can be alternated is limited by the condition that the solvents of the alternating materials need to be orthogonal. Our goal is to deposit the organic DBR completely from the vapor phase by an innovative technique called initiated Chemical Vapor Deposition (iCVD). iCVD does not require the use of solvent and allows precise control over layer thickness by coupling with laser interferometry. The polymers that will be alternated will have a large refractive index contrast, as for example Teflon (n≈1.38) and polystyrene (n≈1.59), so to achieve high reflectivity with a limited number of layers. The surface roughness, interfacial roughness, the thickness and the electron densities of each layer will be characterized by X-ray reflectivity (XRR). The results will be compared with ellipsometry and microscopy data.

Compensation: 6 month / 440€ per month


Contacts:
Dr. Anna Maria Coclite, Assistant Professor
anna.coclite@tugraz.at
Dr. Roland Resel, Associate Professor
roland.resel@tugraz.at

Quantum-Mechanical Modelling of Materials      >> mehr >>

We are currently seeking Master students to work on on the following topics:

* Modeling electronic and structural properties as well as growth of molecules interacting strongly with metal surfaces.
* Design of novel self-assembled monolayers (SAMs) for modifying electrode properties in organic electronic devices.
* Understanding transport through and polarization effects in self-assembled monolayers through quantum-mechanical modelling.
* Computationally designing hybrid systems consisting of nanopatterned ferroelectrics and layered semiconducting materials for novel device applications.
* Impact of Monolayers Inhomogenieties for Hot Spot Formation in Organic Electronic Devices.
* Employing post DFT techniques for reliably modelling charge distribution and electrostatic screening in molecular materials.
* Understanding the electronic properties of weakly coupled hybrid interfaces.
* Predicting the structure of organic adsorbates from first principles.
For further details just come bye and we can identify the topic most interesting to you.
Start: anytime

Contact: Dr. Oliver T. Hofmann (o.hofmann@tugraz.at), Prof. Egbert Zojer (egbert.zojertugraz.at)
Compensation: 440 € per month (Forschungsbeihilfe) for 6-8 months
Additional aspects: work in an internationally very well established group in the area of atomistic modelling of interfaces; publishing in high impact journals; participation in international conferences.