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Abstract

An activated carbon deposition technique based on inkjet printing is proposed for the fabrication of supercapacitors electrodes. By mastering the activated carbon suspension in ethylene glycol through use of a surfactant and by utilizing a substrate treatment with OTS, 10¼m wide structures have been obtained with 50¼m ink jet nozzles.

Abstract

The presented work deals with high-density integrated capacitors for output filters in future micro DC-DC converters. In low power portable applications, integrated passive components are necessary to produce miniaturized systems. When talking about integrated capacitors, the current solutions on silicon (MOS or MIM) are not able to produce the capacitance values required for 1W DC-DC converter: more than 1uF/mm². To increase the capacitance density, the first approach is to work on the capacitor geometry: reduced dielectric thickness and maximised electrodes area. The second approach concerns the use of a high-k dielectric. In the presented work, we are combining these two approaches. 3D capacitors structures were realised with deep cavities network etched by DRIE in a high conductivity silicon substrate. The SiO2/Si3N4 standard dielectric [1] was replaced by ZrO2 (k =25- 40). The ZrO2 films (about 100 nm) were deposited by liquid injection MOCVD from Zr2(OiPr)6(thd)2. The following deposition parameters were studied: oxygen flow (0.05-0.1 l/min), substrate temperature (450°C-550°C), injection frequency (0.5-2 Hz), pressure (1-1000 Pa). The difficulty laid on the necessity to obtain at the same time uniform films (without cracks), good stoichiometry without carbon contaminants and good coverage in the deep silicon cavities. The stoichiometry and carbon contaminant were controlled by XPS, FTIR and SIMS. The ZrO2 thickness was measured by ellipsometry and by SEM on the cross-section of the cavities. The ZrO2 films deposited on silicon (100) were first characterized structurally by XRD. The films were constituted of a mixture of tetragonal and monoclinic phases. The deposition parameters were varied in order to promote the tetragonal phase (permittivity reported around 40 [2]). Low oxygen flow (0.05 l/min), low temperature (450°C), low injection frequency (0.5 Hz), low pressure (< 100 Pa) provided films with a predominant tetragonal phase. In parallel, the 3D coverage was observed in cavities with different depths (from 10 to 30 um) and widths (from 2 to 8 um). The thickness evolution was plotted versus the cavity aspect ratio (depth/width). It was shown that the ZrO2 thickness decreased to 20% - 30% of its surface value when the aspect ratio of the cavity was 2. For aspect ratio higher than 2, the thickness decreased only slightly. Electrical characterization of the ZrO2 films were done on two types of substrates: low resistivity Si (0.2 Ohm.cm) and Pt/Ti/SiO2/Si. The I(V), C(V) and C(frequency) characteristics for different deposition parameters allowed the evaluation of the leakage current (< 10e-6 A.cm-2), the permittivity (around 25), the breakdown voltage (300 kV/cm). These dielectric properties combined with 3D deposition will allow the realisation of very high-density capacitors.

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Abstract

For applications such as computers, cellular telephones and Microsystems, it is essential to reduce the size and the weight of electronic devices. More particularly, this evolution implies the miniaturization of high effi ciency on-chip dc-dc converters providing low voltage to the various ICs. Therefore, fabrication of magnetic components dedicated to power conversion becomes necessary. To miniaturize inductors, the micromachining techniques provide solutions based on low-temperature process compatible with active part of the converter. The proposed inductor topology is based on a spiral-type structure which consists in a copper conductor sandwiched between two CoNiFe (60%- 15%-25%) layers shielding the magnetic fl ux of the inductor winding. Considering a 1-5 MHz operating switching frequency, a laminated core has been investigated in order to reduce eddy-current induced in the core. We have made several investigations on the electroplating baths parameters by changing temperature, pH and current density values in order to obtain optimum magnetic properties (Bsat=2.3T, low Hc, ¼r=250, resistivity>30 ¼Ohm.cm). These proprieties are measured by SQUID and the composition is analyzed using quantitative energy dispersive X-ray analysis. Research reported in this paper is an example relative to the microinductors fabrication for micropower applications. It shows the feasibility of a spiral inductor structure with a laminated core adequate for a high frequency switching operation. The fi nal paper will describe with more details the characterizations of a ten turns prototype exhibiting a 1¼H inductance value.

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Mots-Clés / Keywords