Dan Dascalu

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.

A 3-D Smith Chart Based on the Riemann Sphere for Active and Passive Microwave Circuits

This letter proposes a spherical 3-D Smith Chart suitable for representing both active and passive microwave circuits. Using the mathematical concept of the Riemann sphere, the extended reflection coefficient plane is transformed into the surface of the unit sphere. Since the proposed Smith Chart compiles the whole complex plane, all possible loads are included. A simple graphic tool is thus obtained that successfully unifies active and passive circuits. In addition, lossy lines with complex characteristic impedances can also be represented. The letter presents the 3-D Smith Chart, provides its main governing equations, and also enumerates its more important properties.

New Micro- and Nanoelectrode Arrays for Biomedical Applications

A very simple fabrication technology for a new electrode array architecture with pyramidal micro- or nano-electrodes (ultramicroelectrodes, or UME) is described in this paper. This technology is based on standard processes used in silicon device fabrication such as: silicon etching, metallic and dielectric film deposition. In order to release the dielectric material from the top of the pyramidal electrode, the photolithographic exposure takes place on the whole silicon surface without photolithographic mask. Different applications of these micro- and nano-electrode array in bio-medical field are presented.

Silicon-compatible waveguides used for an integrated opto-mechanical pressure sensor

Abstract We present the investigation of different types of silicon-compatible optical waveguides and the possibility to use them in an opto-mechanical pressure sensor. Silicon-based integrated optics appears as an attractive domain of applications for micromachining and allows the development of micro-opto-mechanical systems (MOEMS). Optical systems integrated on silicon are of special interest because of their process compatibility with CMOS technology. The work is focused on the fabrication of an opto-mechanical pressure sensor based on a Mach–Zehnder interferometer, integrated with photodiodes and diaphragms. Micromechanical, optical and microelectronic structures are fabricated on the same silicon substrate. The mechanical part is a cascade of three diaphragms, made by wet anisotropic etching of the substrate. For optical waveguides we experimented with different materials: Si 3 N 4 , SiON, polyimides, SiC, and amorphous silicon. We investigated the optical properties of these materials, technological processes and the possibility to integrate them in a microsystem.

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.

GaN membrane-supported UV photodetectors manufactured using nanolithographic processes

Membrane GaN metal-semiconductor-metal (MSM) photodetector structures using nanolithographic techniques have been manufactured for the first time. Very low dark currents and unexpected high values for the responsivity have been obtained. It seems that the membrane together with the (submicronic) MSM structure increase the gain of the structure and responsivities in the range of 50-100A/W can be obtained.

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.

GHz FBAR and SAW resonators manufactured ON GaN/Si

This paper presents the manufacturing and the microwave characterization of FBAR and SAW type resonators on GaN thin films grown on a high resistivity (111) oriented silicon subnstrste. The resonators have been manufactured using advanced micromachining technologies (for the FBAR structures)and nanolithographic techniques (for the IDT of the SAW structure). FBAR structures working at frequencies higher then 5 GHz have been obtained. For the SAW type structures a resonance at 4.8 GHz has been obtained for 250nm fingers series connection of the SAWs, and 7.1 GHz for 100–150nm fingers face to face SAW structures.

Phtalocyanine based integrated gas sensor

This paper presents the layout and the technological steps for an interdigitally integrated capacitor used for gas detection. Silicon micromachining technology is applied for manufacturing the sensor substrate. The sensitive layer used is phthalocyanine (Pc) deposed by EDL (evaporated dyes layers technique). Many solutions were found using the phthalocyanine derivatives deposition technique. Considering the different sensitivities of phthalocyanines derivatives, we obtained different gas sensors. The copper phthalocyanine (Cu Pc) and nickel phthalocyanine (Ni Pc) have been investigated for NO/sub x/ detection. The measurement of sensors for NO/sub x/ and NH/sub 3/ detection are presented as concentration versus impedance. The microsensor testing structures deposited with phthalocyanines were investigated by impedance measurements in a vacuum chamber controlled by a gas analyzer. The measurements were made at room temperature but a medium temperature is applied (< 200/spl deg/C) after measurement, for cleaning the material in order to reuse the sensor. The sensor is integrated, MOS compatible, cheap, easy to use and has low power consumption.

Silicon hillocks elimination using a complexant redox alkaline system

This paper present the results from the investigation of the chemical anisotropic etching of single-crystal silicon in the following solutions: KOH, K3[Fe(CN)6] 0.1M, K4[Fe(CH)6] 3H2O 0.1M, KNO3 0.1M and/or complexant added. The complexants added in KOH solution were: Calix(4)arenes, Phenols and Ether Dibenzo 18 Crown 6. The result using also NaOH or LiOH H2O and complexants are presented. The reaction mechanism and the hillocks formation and elimination are analyzed. 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, almost free of hillocks, to utilize the usual mask material resistant at the new etchants.