Si, Ge nanocrystals based dosimeter capacitor


Project Director: Dr. Lazanu Sorina

Project ID: 42PED from 03/01/2017 (PN-III-P2-2.1-PED-2016-0206)

Project Director: Dr. Sorina Lazanu

Project Type: National

Project Program: PED

Funded by: Romanian National Authority for Scientific Research, UEFISCDI

Contractor: National Institute of Materials Physics

Project Status: In progress

Start Date: Tuesday, 3 January, 2017

End Date: Monday, 2 July, 2018

Project Abstract:

The project proposes a new solution of MOS dosimeter, as a capacitor with a structure oxide/Ge or Si ncs layer/oxide/Si wafer with top and bottom metallic contacts, and oxide SiO2 or HfO2. It is aimed to be used as a radiation sensor in space or for medical applications. The proposed device is innovative as the approach is innovative by selecting oxide (SiO2 or HfO2) and (Si or Ge) nanocrystals to be embedded in, by modifying morphology and structure of the layer containing nanocrystals  and in turn changing the deposition and annealing parameters and the thicknesses and stoichiometry of oxides. The feed-back between preparation and characterisation activities is used to maximize the sensitivity to the irradiation dose and the retention time. To prove the concept of the project, a demonstrator of the MOS capacitor-like dosimeter will be manufactured, and validated in laboratory environment, according to TRL3.
The specific objectives of the project are: wdeposition of Ge/oxide and Si/oxide, with oxide SiO2 or HfO2; nanocrystals formation by annealing; correlation of technological parameters with film structure and morphology at different stages; wmanufacturing test samples of trilayer structures with metallic contacts, and testing them for the response to radiation; selection of structures with best response to radiation; w validation of the innovative project concept by manufacturing a demonstrator based on trilayer structures with best response to radiation and retention time; testing the demonstrator according to TRL3; w dissemination and exploitation of the technological and scientific results (patent application, ISI and conference papers) taking into account IPRs; w coordination of activities in order to achieve all project objectives, progress monitoring; continuity of information flow during project unfolding.
By accomplishing all these objectives, the outcome of the project, a new MOS capacitor for dose measurement as demonstrator, is obtained.

Project Objectives: 

The scope of the project is to develop MOS capacitors based on Ge or Si nanocrystals embedded in oxide, to be used as radiation sensors in space or medical applications. The demonstrator of radiation detector that we aim to manufacture has capacitor trilayer structure: oxide/Ge or Si nanocrystals  layer/oxide/Si wafer with top and bottom metallic contacts.

 

Dr. Sorina Lazanu – Project Director

Dr. Magdalena Lidia Ciurea

Dr. Ana-Maria Lepadatu

Dr. Ionel Stavarache

Dr. Catalin Palade

Dr. Valentin Serban Teodorescu

Technician Elena Stan

Second stage (2018): Manufacturing and functional characterization in the laboratory of the demonstrator for dosimeter based on MOS capacitor with Si or Ge nanocrystals.

Summary

In the present stage we aimed to manufacture and test in the laboratory, according to TRL 3, the demonstrator of the dosimeter based on MOS capacitor with Ge nanocrystals embedded in HFO2. The operating principle of the device is the following: NCs are charged, and thus a local electrical field is created. By exposure to radiation, electrical carriers are generated in the oxide, and they are moving in the electric field producing nanocrystals discharging. In its turn, the discharging of nanocrystals produces the modification of the flat-band voltage of the MOS capacitor, which becomes a measure of the absorbed dose.

In the current stage, more activities developed as a direct continuation of the activities started in the previous stage. Thus, we prepared test samples and characterised them electrically and from the point of view of their response to ionizing radiation. In this stage we defined, manufactured and characterised two versions of test samples, one of them proposed in this stage, based on the results obtained previously. The two test samples have different thicknesses of the control HfO2 oxide. Based on the choice of electrical characteristics and of response to ionizing radiation, the best test samples were selected and the demonstrator was defined (oxides, nanocrystals, composition of the intermediate layer, layer thicknesses and preparation conditions).

The demonstrator was manufactured and tested in the laboratory from the point of view of electrical characteristics and sensitivity to ionizing radiation. The obtained device is at the TRL 3 level.

The webpage of the project was updated.

A patent request was addressed to OSIM.

The obtained results are disseminated in 2 communications at International Conferences, and in 2 ISI papers: 1 submitted for publication, 1 in final stage of preparation.

The objectives and activities of the present stage were fully realized.

Results

Demonstrator of dosimeter; working parameters of the demonstrator.

1 patent request addressed to OSIM.

1 ISI paper submitted for publication.

1 lSI paper in final stage of preparation.

2 communications at international conferences (oral presentations)

Delivrables

# demonstrator; # working parameters and characteristics of the demonstrator.

In the present stage we aimed to prepare structures of Si or Ge nanocrystals (NCs) floating gate MOS capacitors, to be used as dosimeters for ionizing radiation. The operating principle of the device is the following: NCs are charged, and thus a local electrical field is created. By radiation exposure, electrical carriers are generated in the oxide, and they are moving in the electric field, producing NC discharging. In its turn, NC discharging produces the modification of the flat-band voltage of the MOS capacitor, which becomes a measure of the absorbed dose.

Structures oxide / Ge or Si in oxide (codeposition) / oxide / Si, with SiO2 or HfOoxide and with different thicknesses were deposited by magnetron sputtering, followed by rapid thermal treatment in different conditions in order to obtain Ge or Si nanostructuring. The structure and morphology were investigated by photoelectron spectroscopy and electron microscopy. Based on the results obtained, 3 types of test samples were prepared: HfO2/Ge NC in HfO2/HfO2/Si; SiO2/Si NC in SiO2/SiO2/Si and SiO2/Ge NC in SiO2/SiO2/Si, having different thicknesses of the three layers, different concentrations of Si or Ge in the oxide, different conditions of thermal treatment. All samples were tested from the point of view of the hysteresis in the C-V dependence, as well as for retention (C-t curves). The best electrical characteristics correspond to the structure with HfO2/Ge NC in HfO2/HfO2/Si. The preparation and characterization of test samples will continue in the next stage of the project.

The structures were characterised from the point of view of their response to ionizing radiation (α and β sources): the dose rate for each of the geometries utilised was calculated, the penetration of the particles in the samples was simulated, and their range calculated. Preliminary measurements of sensitivity of test samples to ionizing radiation were performed, and demonstrator manufacturing started. These activities will continue, with the greatest weight, in the next stage of the project.

The web page of the project was created and updated. The obtained results were disseminated in 1 ISI article and 3 scientific communications presented at international conferences (2 oral and 1 poster).

The objectives and activities of the present stage were fully realized.

Results

Test samples; deposition and thermal treatment parameters; preliminary results on the demonstrator.

1 ISI paper (accepted for publication); 3 communications at international conferences (2 oral presentations, 1 poster)

Delivrables

# trilayer structures SiO2/ Si NCs in SiO2/SiO2/Si & SiO2/Ge NCs in SiO2/SiO2/Si & HfO2/Ge NCs in HfO2/HfO2/Si; # morphology and structure data and images taken on trilayer structures; # test samples; # current voltage (I-V) and capacitance voltage (C-V) characteristics of test samples; # preliminary results on the sensitivity to ionizing radiation of test structures.

List of Publications: 

 

  1. Material parameters from frequency dispersion simulation of floating gate memory with Ge nanocrystals in HfO2, C. Palade, A.M. Lepadatu, A. Slav, S. Lazanu, V.S. Teodorescu, T. Stoica, M.L. Ciurea, Appl. Surf. Sci. 428(2018), 698.

Project Contact Person:

Project Director:  Dr.Sorina Lazanu

National Institute of Materials Physics, Atomistilor 405A., 077125 Magurele - Bucharest, ROMANIA

Tel:+40--(0)21-2418-171

Email: lazanu@infim.ro


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