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Offers : 108

Investigating the polarity related properties of well-ordered ZnO nanowires for piezoelectric devices: The issue of defects & hydrogen

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Start date : 1 October 2019

offer n° LMGP2019-2

Topic:

The development of semiconductor nanowires (NWs) is of great basic and technological interests owing to their high aspect ratio at nanoscale dimensions, giving rise to novel, remarkable properties, as well as a broad range of potential applications. Among them, ZnO as an abundant and biocompatible compound semiconductor with attractive properties has been receiving increasing interest over the last decade. It crystallizes into the strongly anisotropic wurtzite structure, which is both polar and piezoelectric. Its ability to grow as NWs oriented along the polar and piezoelectric ±[0001] (i.e., c) axis by a number of deposition techniques including the low-cost and low-temperature chemical bath deposition is of great importance for its use in nanoscale engineering devices. The efficient integration of ZnO NWs into the engineering piezoelectric devices to name a few requires the precise control of the uniformity of their structural morphology over large surface areas. This is typically achieved by selective area growth using pre-patterned nucleation surfaces by technological processes in a cleanroom environment (i.e. advanced lithography and etching). Two correlated fundamental properties that have crucial effects on the piezoelectric device performances are the polarity and the nature and the defect density. We have shown, for the first time, in 2014 the formation of O- and Znpolar ZnO NWs, opening the way for more deeply analyzing their effects, which are critical as reported in ZnO single crystals and films. Interestingly, the nature and the density of the defects are related to surface terminations at the NW top facet and thus to polarity. However, these characteristics are not known in ZnO NWs, although they drastically govern the performances of the engineering devices. In particular, hydrogen has recently emerged as a major source of defects in ZnO NWs, but very little is currently known about this subject. The thesis project aims at elucidating the present polarity as well as the nature and density of defects (especially defects in connection with hydrogen) on well-ordered O- and Zn-polar ZnO NWs formed by combining selective area growth with chemical bath deposition in LMGP by correlating advanced characterization experiments as transmission electron microscopy, Raman spectroscopy, Fourier Transformed infrared spectroscopy, tunnel microscopy equipped with local probes, X-ray photoelectron spectroscopy with ab initio calculations to simulate the position of H inside the ZnO structure. Following this fundamental investigation, the fabrication of piezoelectric devices will be considered to directly show the beneficial effects on the device performances.

Scientific environment:

The applicant will work in the LMGP, Materials and Physical Engineering Laboratory inside the Nanomaterials and Advanced heterostructures team in close collaboration with the Aristotle university of Thessaloniki, Physics department in Greece for the ab initio calculations and neighbour laboratories in Grenoble (i.e. Institut Néel, …) for specific characterisation techniques. Located in the heart of an exceptional scientific environment, the LMGP offers the applicant a rewarding place to work. LMGP Web Site: http://www.lmgp.grenoble-inp.fr/ PhD thesis duration: 36 months from Fall 2019

Required background:

The applicant should have an Engineering degree and/or a Master of Science in materials physics and chemistry, nanosciences, and/or semiconductor physics. Specific skills regarding team work and English abilities will be required for her/his integration into the team and for taking part in the ongoing international collaborations. Fundings: IMEP-2 Doctoral School (priority PhD thesis topic)

Closing date for applications: 1st of June 2019

  • Keywords : Engineering science, Electronics and microelectronics - Optoelectronics, Materials and applications, LMGP
  • Laboratory : LMGP
  • CEA code : LMGP2019-2
  • Contact : eirini.sarigiannidou@grenoble-inp.fr

Spike based processing chain for signal classification

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Start date : 1 September 2019

offer n° SL-DRT-19-0990

The expansion of the internet of things is conditioned by our ability to develop innovative systems able to apprehend and understand the environment while having an ultra low power consumption, compatible with energy harvesting.

To reach such a goal, one of the solution which is knowing a considerable renewed interest is the use of acoustic signals. Their low frequencies undoubtedly induces a low power consumption in the circuit interface and their low cost eases the dissemination of this solution. There’s a huge applicative potential: wake-up by key words (the well known “ok google”), choc detection, source localization, event classification, surveillance, and machine health monitoring.

In order to implement such complex functions in an energy efficient manner, the potential of neural networks is more and more considered. However today, these solutions are too power consuming. To reduce this power, several alternatives are considered. One of the most promising is the coding of the signal in spike, coherently with neuromorphic architecture. Recently, CEA-LETI has developed a new ADC architecture which directly generate some spike and the best power efficiency in the state of the art has been reached. The aim of this PhD is to follow up this work by implementing in the analog domain some feature extraction in order to reduce the complexity of the neural network processing. To reach the best energy efficiency, a joint optimization between the analog, digital and algorithmic part is mandatory.

In the scope of this PhD, CEA-LETI and EPDFL are collaborating to develop this new analog processing interface, adapted to neural networks based on spike processing. The main objective is ti setup a methodology to reduce the power consumption in all the sensing systems. The automotive applications will be particularly considered. Other application areas and different kind of signal might be also studied.

  • Keywords : Engineering science, Electronics and microelectronics - Optoelectronics, Mathematics - Numerical analysis - Simulation, DACLE, Leti
  • Laboratory : DACLE / Leti
  • CEA code : SL-DRT-19-0990
  • Contact : dominique.morche@cea.fr

Modélisation/caractérisation mécanique et triboélectrique du procédé de nanoimpression en interfaces souples

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Start date : 1 October 2019

offer n° SL-DRT-19-0977

The flexible molds used in nanoimprint lithography allow to reduce the impact of a particle on the defectivity of a patterning step: its flexibility is used to conform the shape of the defects without impacting the surrounding structures. This flexibility is usually obtained by using single-material or composite polymer materials that have the ability to reproduce patterns having critical dimensions of a few tens of nanometers. The state of the art materials can be transformed from a viscous state (and thus able to flow in nanostructures) at room temperature to a state of elastic solid by photo-polymerization at 365 nm while having an anti-adhesive free surface. This elastic state is fundamental for the performance of replications: the material must have sufficient stiffness to prevent buckling or irreversible deformation during the process, but it must have enough flexibility to be demolded from the resin to be printed without damaging the patterns created in the latter. Nevertheless the use of these flexible molds reinforces the appearance of electrostatic charges during the separation of the mold and the substrate. These charges are usually dissipated macroscopically by means of antistatic bars or ionized air jets, but they can persist on the extreme surface of the flexible stamp and cause deformation of the structures. The objective of this thesis is to study through AFM measurements the behavior of these interfaces.

  • Keywords : Engineering science, Metrology, Solid state physics, surfaces and interfaces, DTSI, Leti
  • Laboratory : DTSI / Leti
  • CEA code : SL-DRT-19-0977
  • Contact : hubert.teyssedre@cea.fr

Design and fabrication of miniaturized wireless-powered sensors on flexible substrate

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Start date : 1 October 2019

offer n° SL-DRT-19-0959

The goal of this thesis is to develop a Wireless-powered sensors on flexible substrate. The measured quantity can be the pressure, the temperature, the acceleration, the strain, the magnetic field etc. The M&NEMS technology developed by the CEA-LETI could meet the demands of extreme miniaturization, ultra-low consumption, high performances and low cost.

In order to identify the more suitable M&NEMS sensors a comparative study of the available sensors will be performed. The criteria will include the pairing with an RF antenna for circuit alimentation and information transmission.

The fabrication of the sensor, the antenna and its electronics will be performed on a flexible substrate which will be chosen in function of the application. This work will rely on the Systems Department (DSYS) at CEA-LETI for the design of the antenna and on the packaging 3D laboratory (LP3D) for the fabrication on the flexible substrate.

An innovative actuation principle based on the thermopiezoresistive back-action effect will also be examined in function of the integrated sensor.

  • Keywords : Engineering science, Electronics and microelectronics - Optoelectronics, Materials and applications, DCOS, Leti
  • Laboratory : DCOS / Leti
  • CEA code : SL-DRT-19-0959
  • Contact : alexandra.koumela@cea.fr

Innovative polymer thin films for power electronics

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Start date : 1 October 2019

offer n° SL-DRT-19-0928

Power electronics require the development of smaller and smaller devices that can withstand high currents and high voltages (> 500 V). In particular, the production of high-voltage thin capacitors (300 µm thick) requires the use of dielectric materials with a high breakdown field. This field has been explored for more than 10 years within the passive components laboratory at LETI. The main approach is the reduction of the capacitor sizes by increasing the dielectric constant of the materials, this often being done to the detriment of the breakdown field. The emergence of new markets, such as batteries for electric vehicles, is now pushing developments towards the use of dielectrics with lower dielectric constants but high breakdown field. Ceramics capacitors already exist and meet the specifications for high voltage applications but their size remains a disadvantage for their integration in high-performance circuits. A promising alternative is the use of polymers that can answer to the main challenges: reduction of the thickness by thin film deposition and resistance to high voltages.

The objective of this thesis is to develop, with techniques compatible with the semiconductor industry, polymer thin films capable of withstanding voltages of several hundred volts, to characterize them and to correlate their properties (including breakdown field and permittivity) to the composition and structure of the materials. Chemical Vapor Deposition (CVD) techniques will be favored because they allow conformal deposition of thin insulating layers in 3D structures. This work will take advantages of the solid expertise already acquired by CEA-LETI on the development of thin polymer films by innovative filament-assisted CVD techniques (such as iCVD). The thesis work will include the definition and selection of precursors compatible with the thin film deposition technique and the optimization of the deposition process to obtain materials that can sustain high voltages. The materials will be characterized using a wide range of physico-chemical characterization techniques (ellipsometry, FTIR, AFM, ToF-SIMS, XPS, …). A second part of the work will include the integration of materials in electronic devices and electrical tests of these components in order to highlight the relationships between the characteristics of dielectrics (including the breakdown field) and the microstructure of the polymers. This thesis may also lead to the identification of failure mechanisms in these materials.

This work will be carried out as part of a collaboration between the department of technology platforms and the RF components laboratory of the devices department. Thin film deposition and some characterizations will be carried out in a clean room. The fine characterizations will be carried out in collaboration with experts in materials characterization (nano-characterization platform) and with specialists in the electrical characterization of passive components.

  • Keywords : Engineering science, Electronics and microelectronics - Optoelectronics, Materials and applications, DTSI, Leti
  • Laboratory : DTSI / Leti
  • CEA code : SL-DRT-19-0928
  • Contact : aude.lefevre@cea.fr
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