Porous Silicon Bio-Chemical Sensors
Development of Porous Silicon for Bio-Chemical Sensing Applications
Tech Area / Field
- CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
- INF-ELE/Microelectronics and Optoelectronics/Information and Communications
- INF-SIG/Sensors and Signal Processing/Information and Communications
3 Approved without Funding
Engineering Academy of Armenia, Armenia, Yerevan
- National Centre for Scientific Research "Demokritos" / Institute of Microelectronics, USA, GA, Athens\nNational Research Council Canada / Institute for Microstructural Sciences, Canada, ON, Ottawa\nMarshall University, USA, WV, Huntington\nUniversity of Toronto / University of Toronto at Mississauga, Canada, ON, Mississauga\nUniversity of Hyogo / Graduate School of Engineering, Japan, Hyogo\nUniversity of South Florida / College of Engineering, USA, FL, Tampa\nUniversity of California / Henry Samueli School of Engineering and Applied Science, USA, CA, Los-Angeles\nConsiglio Nazionale Delle Ricerche / Istituto per la Microelettronica e Microsistemi, Italy, Napoli\nKorea University, Korea, Seoul\nUniversity of Montreal, Canada, QC, Montreal\nUniversita di Pisa / Dipartimento di Ingegneria dell' Informazione: Elettronica, Informatica, Telecomunicazioni, Italy, Pisa\nUniversidad Autonoma de Madrid / Facultad de Ciencias, Spain, Madrid
Project summaryThe Scientific and Technological Objectives of this Project are:
- Formation and research of porous silicon (PS) with size and properties adequate for bio-chemical sensing applications. The PS fabrication process investigation should give insight into pore formation, diameter, and propagation depth of the membrane, as well as sidewall quality. This can be related to the formation conditions of PS layers.
- Development of new structure and technology for fabrication of PS-based bio-chemical sensors, which are compatible with silicon technology and have enhanced stability and selectivity through PS post-formation treatment.
Bio-chemical sensors have an important and growing role in perse fields including medical diagnosis, drug development, homeland security, and manufacturing.
This Project is focused on a pre-existing PS formation process, with potential to become advanced PS-based sensor, capable of detecting biological agents and organic solvents through electrical properties (capacitance and conductance). Our theoretical estimates and preliminary laboratory investigations reveal the main problems that require further solutions. Problems are the following:
- Small scale of PS formation. There are no commercially available materials suitable for its applications. Solution of the problem will be intended via electrochemical anodization of silicon wafers with pulse current (that allows periodically separate layers of PS and renew the silicon surface continuously). This formation method provides an excellent control over the porosity and thickness of the inpidual layers.
- Problem of stability of PS. In fresh form it is easily oxidized to inert porous oxide matrix. There are derivatization schemes to passivate the surface of PS but these schemes yield different artifacts and the impact of passivation layer onto chemical and electrical properties of PS is not studied profoundly enough. Solution of problem will be in testing available derivatization schemes (in organic solvents and other liquid substances, as well in gaseous ionized environments).
- Problem of sensitivity of PS. In an effort to increase sensitivity, PS layers can be modified in various ways, one of which being polymer deposition. A wide range of polymers is available, differing in both size and chemical properties such as solubility in the substance to be measured and even physical properties such as conductivity. This opens many possibilities to tune the sensor by making use of the polymer properties.
- Problem of producing of PS with uniform sizes and shapes. This is also the problem of great importance as for bio-chemical applications regularity of sizes and shapes is of paramount importance. This problem will be tentatively solved together with those mentioned in problem 1 by using equal size grains of silicon or formation and cutting of sub-layers of PS of equal thickness.
Main bottleneck to be resolved during the production of PS-based sensors is formation of electrical contact, having no influence on the sensitivity of sensors. This problem can be solved by means of creating back electrical contact on PS layers. Use of unilateral back contact allows a complete exposure of the surface to the sensing species and reduces the generation of ionic currents through the porous matrix. Therefore, sensors will have metal-Si-PS structure. It is necessary to mention that earlier we have developed such construction and technology for PS-based solar cells and power transistors.
We will present a full characterization of PS-based electrical sensors in terms of its sensitivity, selectivity, and response speed. First we will test our sensors with DNA and organic solvents (ethanol, acetone, benzene, toluene, dimethylformamide). In future the detection scheme has also been extended to include the detection of viral DNA, proteins, and potentially bacteria. This Project will lead to the development of a “smart bandage”, where the detection of bacteria or viruses can be diagnosed and an antibiotic treatment can be recommended.
Our comprehensive study is anticipated to extend the understanding of the fundamental nature of bio-chemical agent’s detection by PS. Specifically, we shall investigate the relationship between the processing treatment and its effect on the electrical properties of the PS layers. This part of the study should provide information on the existing physical and chemical mechanisms in this material. The study will help to establish the usefulness of PS in bio-chemical sensing metal-Si-PS structures.
Working plan includes 4 Work Packages:
- Formation of PS layers with size and properties adequate for bio-chemical sensing applications.
- Modification of the composition and properties of PS.
- Exploration of the kinetics and physical mechanisms of bio-chemical agent’s detection by PS.
- Standardization, management and control.
Work packages are interconnected and form a robust and complete set of actions aimed at achievement of the Project objectives. The main practical result of the Project will be the development of engineering prototypes of portable, hand-held diagnostic device and the study of their properties. Such sensitive label-free devices can be used to detect the presence of specific biological agents or organic solvents.
For the theoretical investigations accompaniment to all studies of Project the standard methods of mathematical physics, physical chemistry, solid-state and microelectronic technology for the control and characterization of PS layers will be used. Regular technological equipment for fabrication and testing of semiconductor devices will be used.
Following properties of obtained PS layers will be studied: composition, impedance of metal-Si-PS structures, surface homogeneity and roughness. Investigation of PS layers porosity will be carried out by liquid displacement device (our patented method). The structural, mechanical and electrical properties of the PS layers will be characterized by a wide variety of techniques:
- Structural - X-ray diffraction, Raman, SPM, SEM, TEM, IR spectroscopy, ESCA.
- Mechanical - Four point bend tests, finite element analysis, optical interferometry.
- Electrical - I-V, C-V, ESR, TOF.
Electrical properties of obtained sensors will be studied. We have developed a novel approach to measure the changes in capacitance (C) and conductance (G) of PS. Using a simple electrical setup consisting of an LCR (Inductance-Capacitance-Resistance) meter and a LabView based computer interface we are able to perform simultaneous measurements of C and G in real time.
Project participants have necessary equipment and significant experience in design and fabrication of semiconductor devices and microchips using silicon and silicon carbide technologies. There is also a significant experience in fabrication and investigation of PS layers and PS-based devices: power transistors, solar cells and sensors. The structural, mechanical, optical and electrical properties of oxidized and non-oxidized PS-based structures were investigated. Participants of this Project have already got several patents in the basic issues of the Project.
Collaboration with foreign scientists and specialists for joint modification, testing and demonstration of our technology, as well as design of final product (sensor) will be very useful for us. Foreign collaborators may participate in fabrication of PS structures, as well as in the investigation of the electrical and other sensorial properties of these structures and bio-chemical sensors. The role of foreign collaborators is also to discuss the problems and to exchange information, obtained during the implementation process of the Project, to take part in scientific seminars and conferences, organized by the executor. They may also assist the commercialization of the obtained results and their advance to the market.
Realization of the Project will make it possible to solve a set of problems, which correspond to the purposes of ISTC:
- reorientation of high-qualified scientific stuff, engineers and technical workers, being previously working in the sphere of armament, to solving peace problems;
- provision of scientists with an alternative peaceful job;
- further integration of scientists, working in the sphere of armament, with the international society of scientists; there will be developed traditional cooperation with the organizations and universities of CIS;
- development of science-consuming technologies in Armenia; etc.
The Project will result in new scientific results and technical patent will be filed. Scientific results will be disseminated through the publications in scientific peer-reviewed journals and presentations in international conferences.
Main statements of the Project were presented in NSTI Conference on Nanotechnology, Biotechnology and Microtechnology (Boston, May, 2006) and in NATO-ASI Workshop on Sensing and Imaging in Medicine, Environment, Security & Defence (Ottawa, October, 2006).
The Project is absolutely original in its tasks and methods to achieve them with no interference with any existing activities of other research teams.
The International Science and Technology Center (ISTC) is an intergovernmental organization connecting scientists from Kazakhstan, Armenia, Tajikistan, Kyrgyzstan, and Georgia with their peers and research organizations in the EU, Japan, Republic of Korea, Norway and the United States.
ISTC facilitates international science projects and assists the global scientific and business community to source and engage with CIS and Georgian institutes that develop or possess an excellence of scientific know-how.