Rodica Iosub

Anisotropic etching of silicon in a complexant redox alkaline system

Abstract This paper presents the results from the investigation of the chemical anisotropic etching of single-crystal silicon 〈100〉 in the following solutions: KOH, K3[Fe(CN)6] 0.1 M, K4[Fe(CN)6] · 3H2O 0.1 M, KNO3 0.1 M and or complexant added. The complexants added in KOH solution were: calix[4]arenes, phenols and ether dibenzo-18-crown-6. The reaction mechanism, the etch rate, the roughness and the hillocks are analysed. The results allow us to use the redox system and/or the organic complexants to monitor the etching process, to obtain a smooth silicon surface with increased etch rate and to utilize the usual mask material resistant at the new etchants.

Silicon membranes fabrication by wet anisotropic etching

Abstract The anisotropic etching of silicon became a key technology for sensor fabrication due to the strong dependence of the etch rate on crystal orientation which offers the possibility of 3D structuring. The paper presents the investigation of anisotropic etching of silicon in organic (ethylenediamine pyrocatechol (EDP)) and inorganic (KOH, KOH+complexant) solutions for sensor membrane fabrication. The protection of metallic layer during the anisotropic etching is considered. The solutions were analyzed and compared in point of view of etch rate and quality of silicon etched surface. The mask materials resistant at etching solutions are presented. The improvement of the anisotropic etching process is realized by using organic complexants added at KOH, which increases the etch rate and minimizes the hillocks formation. The EDP etching is analyzed for metallic layer protection and contamination avoidance. New materials obtained at low temperature deposition (

A Sensitive capacitive immunosensor for direct detection of human heart fatty acid-binding protein (h-FABP)

The fabrication of a capacitive interdigitated immunosensor (CID) based on a mixed self-assembled monolayer (mSAM) film for the direct detection of heart fatty-acid binding protein (h-FABP) without any labeling is described. The capacitance changes of mSAMs vs. homogenous ordered self-assembled monolayers (hSAMs) on gold work electrodes/covalently bonded antibodies/buffered medium are utilized for monitoring the specific antibody-antigen interaction. Capacitance measurements in the absence and presence of Faradaic currents were performed. The electrochemical properties of mixed monolayers were compared with those of a pure monolayer of 11-mercaptoundecanoic acid (MUA) self-assembled on gold surfaces. Taking into account the stability of the studied monolayers during the electrochemical experiments with the Faradaic process, the best SAM functionalization method was used for developing a sensitive capacitive immunosensor with a non-Faradaic process for direct immune detection of human h-FABP. Under the optimized conditions, the proposed mixed self-assembled monolayer (mSAM1) on gold electrode exhibited good insulating properties such as a capacitive behavior when detecting h-FABP from human serum in the range of 98 pg ml(-1)-100 ng ml(-1), with a detection limit of 0.836 ng ml(-1) comparative with a homogenous self-assembled monolayer (hSAM).

Micromachining of a silicon multichannel microprobe for neural electrical activity recording

The cellular potential recording permits the investigation of the central nervous activity. The paper presents the design and manufacturing steps of an eight-channel microprobe for recording the electrical activity of neural cells and tissues integrated on the same chip with the electronics. The specific fabrication processes of the integrated microprobe are presented. An implantable neural microprobe is developed to enable the correlation between electrical activity in the human nervous system and externally psycho-electrical stimuli.

Silicon micromachined sensor for gas detection

The paper presents the layout and the technological steps for an interdigitated integrated capacitor used for gases detection. Silicon micromachining technology is applied for manufacturing the sensor substrate. The sensitive layer used is phthalocyanine (Pc) deposed by evaporation technique under high vacuum. The phthalocyanine derivatives are obtained by the same deposition technique. Considering the different sensitivities of phthalocyanines derivatives, we obtained different gas sensors. The copper phthalocyanine (CuPc), nickel phthalocyanine (NiPc) and iron phthalocyanine (FePc) have been investigated for NO x detection. The measurement of sensors for NO, and NO 2 detection will be presented as gas concentration versus impedance. The microsensors testing structures deposited with phthalocyanines were investigated by impedance measurements in a vacuum chamber controlled by a gas analyser. The measurements were made at room temperature but a medium temperature is applied (<200 °C) after measurement, for cleaning the material in order to reuse the sensor. The sensor is integrated, MOS compatible, cheap, easy to be used and has a low power consumption.

ISFET Microsensors HfO2 Based for Biomedical Applications

The sensor presented in the paper is based on ion selective field effect transistors to detect chemical quantities from biological media (Arshak Poghossian, 2004). The micromachining techniques used for realisation of the chemical sensors dedicated to pH, Na+, K +, H+ detection using silicon micromachined transducers and sensitive layers as HfO2 are presented. The silicon transducers are realised by micromachining techniques (both surface and bulk) and the sensitive layer (in the area of nm thickness) is deposited on top of the wafers allowing the sensors HfO2 based realisation. HfO2 is a material characterised by high dielectric constant and its characteristics in terms of gate material for ISFET sensors are presented. The electrical and functional characterisation of sensors are presented. The major achievements of the work are: manufacturing a CMOS compatible ISFET based on chemical sensitive layers for biological and medical applications; integration of the ISFET sensors on the tip of a microprobe that can be used for measurements of different chemical species (pH, Na+, K+ , H+) in vivo and in vitro and the development of a new sensing material (HfO22); compatibility of all technological process with CMOS technologies and development of new packaging methods

Simulation, design and microfabrication of multichannel microprobe for bioelectrical signals recording

The extracellular potential simultaneous recording permits the investigation of the central nervous activity. The paper presents the design and manufacturing steps of a five electrodes microprobe for recording the electrical activity of neural cells and tissues integrated on the same chip with the electronics. The specific fabrication processes of the integrated microprobe are presented. An implantable neural microprobe is going to be developed to enable the correlation between electrical activity in the human nervous system and externally psychoelectrical stimuli. The electronics accomplish the separation and reduction of the biological noise recording.

Elimination of silicon hillocks using an alkaline complexant etching system

Abstract This paper presents the results obtained in silicon hillock elimination using alkaline solutions: KOH, NaOH, LiOH·H 2 O with an added complexant. The added complexant in alkaline solutions is azocalix[4]arene. The alkaline solutions were compared and analysed with and without added complexant for their effect on hillocks. The behaviour of these solutions is explained using the theory of molar conductivity. The results show that use of the complexant permits control of the etching process, yielding a smooth silicon surface, almost free of hillocks. A comparison between the alkaline etchants (KOH, NaOH, LiOH·H 2 O) is made and the influence of the cations in silicon etching process is explained.

Differential Piezoresistive Pressure Sensor

The pressure microsensor presented in this paper is based on a thin, elastic membrane, with boron implanted piezoresistive elements included, positioned in the maximum mechanical stress areas on the membrane. The pressure range for the developed sensors is in the 0divide400 mbar range, and this is the main novelty of this device. The optimized design and technological steps offer high efficiency, sensitivity and reliability to the developed pressure sensor.

The mechanism of anisotropic etching of silicon in a complexant alkaline system

This paper presents the results of the study and experiments of the chemical anisotropic etching of silicon in a complexant alkaline system (KOH 4.5 M and complexants added). The great results obtained using calix[4]arene like complexant make necessary the study of the mechanism of the silicon etch rate increasing and of the roughness minimizing. A new macrocyclic complexant (azocalix[4]arene) and indicator of pH for silicon etching solution, the etch rate and the roughness are analysed. The complexant alkaline system for anisotropic etching of silicon is an absolutely original idea of the authors.