Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-10-22
2001-03-06
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S304000, C429S236000, C429S231100, C029S623100
Reexamination Certificate
active
06197450
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to thin film micro-electrochemical energy storage cells (MEESC), such as microbatteries and double-layer capacitors (DLC).
BACKGROUND OF THE INVENTION
Advances in electronics have given us pocket calculators, digital watches, heart pacemakers, computers for industry, commerce and scientific research, automatically controlled production processes and a host of other applications.
These have become possible largely because we have learned how to build complete circuits, containing millions of electronic devices, on a tiny wafer of silicon no larger than 25-40 mm square and 0.4-0.5 mm thick. Microelectronics is concerned with these miniaturized integrated circuits (ICs), or “chips” as they are called. In a circuit, electrical energy is supplied from, for example, a microbattery or a double-layer capacitor (DLC) and is changed into other forms of energy by appliances in the circuit, which have resistance.
Recently, with the tendency of miniaturizing of small-sized electronic devices, there have been developed thin-film microbatteries, which have several advantages over conventional batteries, since battery cell components can be prepared as thin (1-20 &mgr;m) sheets built up as layers. Usually, such thin layers of the cathode, electrolyte and anode are deposited using direct-current and radiofrequency magnetron sputtering or thermal evaporation.
The area and thickness of the sheets determine battery capacity and there is a need to increase the total electrode area in a given volume. Thin films result in higher current densities and cell efficiencies because the transport of ions is easier and faster through thin-film layers than through thick layers.
U.S. Pat. Nos. 5,338,625 and 5,567,210 describe thin-film lithium cells, especially thin-film microbatteries having application as backup or primary integrated power sources for electronic devices and method for making such. The batteries described in these references are assembled from solid state materials, and can be fabricated directly onto a semiconductor chip, the chip package or the chip carrier. These batteries have low energy and power. They have an open circuit voltage at full charge of 3.7-4.5 V and can deliver currents of up to 100 &mgr;A/cm
2
. The capacity of a 1 square cm microbattery is about 130 &mgr;A/hr. These low values make these batteries useful only for very low power requirements in some microelectronic circuits.
A double-layer capacitor (DLC), as opposed to a classic capacitor, is made of an ion conductive layer between two electrodes. In order to make an electric double-layer capacitor smaller and lighter without any change in its capacitance, it is necessary to increase the energy. This may be accomplished, for example, as described in U.S. Pat. No. 5,754,393, by increasing the working voltage by use of an electrolyte having a high decomposition voltage.
Advanced etching technologies, such as reactive-ion etching (RIE), electron-cyclotron-resonance (ECR) etching and inductively coupled plasma (ICP) etching have been developed to etch semiconductor devices having extremely small features sizes. By using the ICP technique it is possible to etch small diameter through-cavities such as through-holes with a very high aspect ratio and smooth surfaces in a substrate such as a silicon wafer.
The present invention is based on a novel approach, according to which a thin-film micro-electrochemical energy storage cell (MEESC) such as a DLC or a microbattery is created on a macroporous substrate, thus presenting increased capacity and performance. By using the substrate volume, an increase in the total electrode area per volume is accomplished. The cavities within a substrate are formed by deep wet or dry etching of the substrate. For example, holes may be formed by an Inductive Coupling Plasma (ICP) etching using the Bosch process described in U.S. Pat. No. 5,501,893.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a micro-electrochemical energy storage cell (MEESC) such as a DLC or a microbattery exhibiting superior performance as compared to such cells known in the art. A more particular object of the invention is to provide a DLC or a microbattery with up to two orders of magnitude increase in capacity.
The above objects are achieved by the present invention, wherein a thin-film MEESC is formed on a substrate having etched structures. The use of such a substrate increases the available area for thin film deposition, thus leading to an increase in volume, i.e. capacity of the cell.
Thus, the present invention provides a thin-film micro-electrochemical energy storage cell (MEESC) comprising two thin layer electrodes and intermediate to these electrodes, a thin layer of a solid electrolyte consisting of an ionically conducting or electronically non-conducting material such as glass, polymer electrolyte or polycrystalline material, and optionally a fourth thin current collector layer, all these layers being deposited in sequence on a surface of a substrate, wherein the MEESC is characterized in that the substrate is provided with a plurality of cavities with high aspect ratio; said electrodes, solid electrolyte and current collector layers being deposited also throughout the inner surface of said cavities and on both surfaces.
In a preferred embodiment the MEESC of the present invention is a thin film microbattery which comprises:
a thin layer anode consisting of alkali metal (M), alkali metal alloy, for example alkali metal alloy based on Zn, Al, Mg, or Sn or in the charged state consisting of lithiated carbon or graphite,
a thin layer cathode consisting of LiCoO
2
, LiNiO
2
, LiMn
2
O
4
, TiS
2
, V
2
O
5
, V
3
O
8
or lithiated forms of the vanadium oxides,
a solid electrolyte intermediate to the anode and cathode layers, which consists of a thin layer of an ionically conducting or electronically non-conducting material such as glass, polymer electrolyte or polycrystalline material, and
optionally, a current collector layer; the anode or cathode layer being deposited on a surface of a substrate, the microbattery being characterized in that the substrate is provided with a plurality of cavities with high aspect ratio; said anode, cathode and solid electrolyte layers being deposited also throughout the inner surface of said holes.
In cases wherein the microbattery is a lithium ion type, such a battery is fabricated in the discharge state where the cathode is fully lithiated and the alloy, the carbon or the graphite anode is not charged with lithium.
According to another preferred embodiment, the MEESC of the present invention is a double-layer capacitor (DLC), which comprises two electrodes made of high surface area carbon powder and intermediate to these electrodes a solid electrolyte layer, preferably a polymer electrolyte.
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patent: 5019468 (1991-05-01), Miyabayashi
patent: 5162178 (1992-11-01), Ohawa et al.
patent: 5187564 (1993-02-01), McCain
patent: 5421083 (1995-06-01), Suppelsa et al.
patent: 5545308 (1996-08-01), Murphy et al.
patent: 5916514 (1999-06-01), Eshraghi
patent: 0 331 342 (1989-09-01), None
patent: 2 550 015 (1985-02-01), None
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patent: 2 621 174 (1989-03-01), None
patent: 2 161 988 (1986-01-01), None
Lehman et al., Thin Solid Films, vol. 276, Issue 1-2, pp. 138-142, Apr. 1996.
Patent Abstracts Of Japan, Publication Number 091186461, Publication Date Jul. 15, 1997.
Haronian Dan
Nathan Menachem
Peled Emanuel
Browdy and Neimark
Chaney Carol
Ramot University Authority for Applied Research & Industrial Dev
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