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Offers : 49

3D reconstruction of nanometric objects from stereoscopic electron microscope images

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Start date : 1 October 2019

offer n° SL-DRT-19-0588

Keywords : Images treatment, GPU programmation, optimisation, inverse problem, stereovision, neural networks.

Robust, non-destructive and fast 3D metrology is a world-wide major challenge of microelectronics industry for defects inspection, optical lithography fidelity and process control. Fast reconstruction methods from stereoscopic electron microscope (SEM) images based on geometrical considerations allow to reconstruct 3D topography of micronic objects. However, those technics cannot be applied on nanometric objects because of local physical phenomena which disturb the placement of the points of interest [2]. Alternative methods based on the resolution of inverse problem have been already prototyped. Significant improvements of the computation time are expected after their implementation on the GPUs of our group. Model calibration methods must also be developed, potentially based on neural networks.

3D metrology based on SEM images arouses the interest of several LETI industrial partners, and this thesis is intended to be a key element for present and future collaborations in this field.

The objective of this thesis is to develop a 3D metrology from SEM images the most precise and robust as possible. For this, the PhD student will initially use the group’s theoretical and simulation resources to improve and develop new SEM imaging models. The scope of these models is broad, from the simulation of micrometric objects to nanometric structures. CEA-LETI has a new generation of SEM that allows to image patterns at different points of view. These multi-stereo images allow an increase of data on the image structure which facilitates its 3D reconstruction, compared to the case of a single SEM image taken in top view.

The PhD student will train the SEM models with a collection of stereoscopic SEM images of patterns, which 3D topographies will be known from reference 3D metrology. The student will investigate, in a second time, different mathematical strategies for the 3D reconstruction, allowing fast and precise convergence.

Eventually, 3D reconstruction will be applied on different customer products of interest.

  • Keywords : Engineering science, Mathematics - Numerical analysis - Simulation, Solid state physics, surfaces and interfaces, DTSI, Leti
  • Laboratory : DTSI / Leti
  • CEA code : SL-DRT-19-0588
  • Contact : aurelien.fay@cea.fr

Van der Waals epitaxy of CdTe on 2D materials

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Start date : 1 October 2019

offer n° SL-DRT-19-0887

2D materials nowadays attract a great amount of research because of their unique properties directly derived from their graphene-like electronic structure and crystalline organization. These materials have strong in-plane chemical bounds while extremely weak, van der Waals type, out-of-plane interaction describing them a 2D sheets of monolayer material. 2D material epitaxy on conventional 3D semiconductors may thus occur without any lattice parameter mismatch strain. The opposite is also true when depositing a 3D onto a 2D. The PhD work consists in studying in details these new epitaxial systems with the proposal of realizing the strain free epitaxial growth of photovoltaics CdTe or infrared sensitive HgCdTe on 2D layers. These materials (2D and 3D) will be grown by molecular beam epitaxy allowing for an in-situ control of the interface. The growth mode of 3D(CdTe)/2D and 2D/3D(HgCdTe) will be first independently studied with the goal of providing a full 3D(CdTe)/2D/3D(HgCdTe) heterostructure where the 3D(CdTe) will promote, through the very thin 2D, the crystalline structure and orientation for the ultimate growth of HgCdTe. Inserting a weakly bonded 2D material also offer promising new functions by enabling the HgCdTe layer to be detached and transferred onto another substrate opening the way towards new optoelectronic applications. The thesis scientific environment will be brought to a broader range by considering the availability and proximity of the nano-characterization platform (CEA-PFNC) where skilled teams and last generation of equipment are dedicated to revealing the chemical nature and crystallographic structure of the epitaxial stacks.

  • Keywords : Engineering science, Materials and applications, Solid state physics, surfaces and interfaces, DTSI, Leti
  • Laboratory : DTSI / Leti
  • CEA code : SL-DRT-19-0887
  • Contact : philippe.ballet@cea.fr

Study and design of an integrated system for the automatic calibration of dispersions within a transducers array and application to a PMUT array

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Start date : 1 September 2019

offer n° SL-DRT-19-0293

The purpose of this thesis is to study and design an integrated electronic system dedicated to the automatic and continuous compensation of dispersions within a MEMS (Microelectromechanical Systems) array.

With the dissemination and the continual expansion of Internet of Things (IoT) and Cyber-Physical Systems (CPS), man-machine and machine-machine interfaces require increasingly efficient and sophisticated sensors. In addition to advantages in cost, reliability, size and power consumption, MEMS based transducers enable sensors to integrate more and more intelligence in their front-end electronics. They also allow innovative topological configurations giving access to measurement ranges that are not addressable by their discrete counterparts.

Arrays of MEMS based transducers enable the spatial discretization of the transduction surfaces and improve the measurements yields and accuracies (gas detector, mass spectrometry, pressure distribution, etc.). They also enable the resolution improvement of electromagnetic and acoustic beams (location, navigation, communication, etc.).

Despite the considerable technological advancements that MEMS are continually enjoying, some application requirements are beyond the transducers intrinsic performances. It is then necessary to implement calibration systems to correct the transducers biases introduced during manufacture or evolving with the operating conditions.

The evaluation and compensation of these errors requires costly calibration process in a dedicated test laboratory, that are not compatible with massive production.

The aim of this thesis is to achieve an integrated electronic diagnostic alternative, an electromechanical BIST (Built-In Self-Test) specific to transducers arrays, combined with an automatic correction system, which will operate in coexistence with the main functions of the sensor interface.

The proposed use-case is that of PMUT (Piezoelectric Micromachined Ultrasonic Transducer) arrays. These devices offer alternatives and complementary solutions to electromagnetic sensors for detection and localization [1], gesture recognition [2] or wake-up signals detection [3]. For most applications, these resonant transducers operate in transmit / receive modes (TX / RX) and need to be actuate at their resonance frequency to optimize the transmission power. The emitted and received beam is focused and steered by phase control.

Errors and dispersion in the PMUT characteristics generates biases in their resonant frequency, gain and quality factor, leading to losses and distortions in the emitted and received beams. For example, a few percent of dispersions on the mechanical stiffness of the transducers can lead to several tens of percent loss on the acoustic power transmitted to a target.

As a first step, the doctoral student will get familiar with the quantities and physical phenomena characterizing PMUT arrays. Based on an analytical model developed within the host laboratory, he will be able to understand the sensitivities to dispersions and their impact on the beam power and directivity.

He will then define the electronic methods and architectures that will allow the system to converge towards the optimal operating conditions, for example by identifying the average resonance frequency of the array the required phase and gain correction coefficients to allocate to each transducer.

The architecture and implementation choices must allow the system to adapt itself according to dispersions and drifts in a continuous and autonomous way, without disrupting the main measurement functions.

The chosen solution will be implemented and validated in a mixed design environment in order to result in a functional demonstrator.

[1] Przybyla, R. J., Tang, H. -., Guedes, A., Shelton, S. E., Horsley, D. A., & Boser, B. E. (2015). 3D ultrasonic rangefinder on a chip. IEEE Journal of Solid-State Circuits, 50(1), 320-334.

[2] Ling, K., Dai, H., Liu, Y., & Liu, A. X. (2018). Ultragesture: Fine-grained gesture sensing and recognition. Paper presented at the 2018 15th Annual IEEE International Conference on Sensing, Communication, and Networking, SECON 2018, 1-9.

[3] Yadav, K., Kymissis, I., & Kinget, P. R. (2013). A 4.4-µ W wake-up receiver using ultrasound data. IEEE Journal of Solid-State Circuits, 48(3), 649-660.

  • Keywords : Engineering science, Electronics and microelectronics - Optoelectronics, Metrology, DACLE, Leti
  • Laboratory : DACLE / Leti
  • CEA code : SL-DRT-19-0293
  • Contact : gwenael.bechet@cea.fr

MEMS mirror for LIDAR in autonomous vehicules

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Start date : 1 September 2019

offer n° SL-DRT-19-0521

Optical MEMS (MOEMS) are more and more asked, in particular for the autonomous car, which has to have mapping possibilities in order to detect obstacles (like a LIDAR – “LIGHT Detection And Ranging”). It consists in scanning the environment with a laser beam and in measuring the distance between the LIDAR and the point where is reflected the laser. A micro-mirror can fill advantageously this function, assuring compactness of the system and low production cost.

The goal of this thesis consists in developing a 1D and 2D micro-mirror able to scan the space following two perpendicular directions, in particular for the LIDAR application. For that purpose, first it will be necessary to study the state of the art on micro-mirrors, to understand the specifications linked to the focused application. From these specifications, the candidate will have to investigate the actuation principle (preferentially piezoelectric). After these preliminary studies, and in parallel of the experimental study of 1D micro-mirrors already developed in CEA-LETI, the candidate will have to work on the analytical modelling, and/or the Finite Element Method (FEM) simulation using COMSOL, of new 1D and 2D micro-mirror architectures. The technological realization of demonstrators will be assured by the technological platform of the CEA-LETI. The candidate will participate in the follow-up of the manufacturing and then will performed the electromechanical and optical characterizations of the devices, in order to compare them with specifications. Finally, the student will propose all the optimization and new architectures in order to improve the performances of the devices.

  • Keywords : Engineering science, Electronics and microelectronics - Optoelectronics, DCOS, Leti
  • Laboratory : DCOS / Leti
  • CEA code : SL-DRT-19-0521
  • Contact : laurent.mollard@cea.fr

Improvement of performance X and gamma-ray imaging by identification of semiconducting detector parameters

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Start date : 1 October 2019

offer n° SL-DRT-19-0796

Our laboratory designs X and gamma-ray imaging systems for medical imaging or luggage control. We use CdTe or CdZnTe-based detectors that are sensitive to five physical parameters of the interaction: deposited energy E, interaction time T and the 3-dimensional position XYZ. These parameters are estimated by real-time analysis of anode electronics signals.

These detectors have been significantly improved in recent years but some limits remain, especially those due to the non-uniformity of the response due to physical properties of the material. The goal of this Ph.D. internship is to overcome these limits by a detailed modelling and characterization of the actual detector response. The identification of internal physical parameters of the detector would allow to optimize estimation of interaction location, time and energy.

The student should have a background in mathematics, statistics or physics and a high affinity for multi-disciplinary research.

  • Keywords : Engineering science, Electronics and microelectronics - Optoelectronics, Instrumentation, DOPT, Leti
  • Laboratory : DOPT / Leti
  • CEA code : SL-DRT-19-0796
  • Contact : gmontemont@cea.fr
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