Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Flat-type unit cell and specific unit cell components
Reexamination Certificate
2000-06-29
2002-08-13
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Flat-type unit cell and specific unit cell components
C429S218100, C429S223000, C429S247000, C429S251000, C429S252000
Reexamination Certificate
active
06432577
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to an apparatus and method for fabricating a microbattery, and more particularly to a planar microbattery using silicon substrates as the structural foundation. With the use of advanced semiconductor packaging techniques, such a microbattery enables the fabrication of autonomous, highly functional, integrated Microsystems having broad applicability. Microsystems technologies seek to develop complex systems-on-a-chip that can sense, think, act, and communicate with their external environment without the need for external hardware. Past developments have emphasized microelectrical and micromechanical component technologies. However, to combine this functionality in an integrated microelectromechanical system (MEMS) requires a compatible power source, such as a microbattery, to power it as an autonomous unit.
Power and structure are areas where these integrated microsystems technologies can have significant impact. The power supply, consisting of energy conversion, energy storage and power management and distribution (PMAD), is an essential and enabling technology for these applications. Unfortunately, it is also often a limiting one, ultimately adding significant weight and volume to the structures. This shortcoming is exacerbated by the advance toward micro
ano-structures since the relative proportion of inactive battery materials, such as the battery container, i.e. the structure to house it, increase significantly with size reduction. Similarly, the structural elements of the finished system/device, while necessary, make significant contributions to the final weight and volume, and the relative proportion of weight and volume of this inactive element will increase with size reductions.
Development of an Integrated Hybrid Power Structure (I-HPS) incorporating energy storage, energy conversion, PMAD, and structure, into a single integrated unit will lessen the impact that these individual components have on the final weight and size of the structure. The I-HPS will significantly reduce the overall size and weight of micro
ano-structures. For example, thin structural frames, fabricated from silicon, may incorporate solar cells on one surface and PMAD elements on the opposing surface. Within the frames themselves, the energy storage element (e.g. lithium-ion batteries) will be accommodated to form a package providing structural and power capabilities.
Silicon (Si) is an ideal candidate for use as a structural foundation for autonomous, mesoscopic systems due to its high strength to density ratio of 3.0 Gpa/g/cc, an order-of-magnitude higher than titanium, aluminum, or stainless steel. Silicon also demonstrates favorable thermal, optical, and electrical properties and has well-defined microelectronic processing properties. Using Si substrates a structure that can simultaneously act as a structural element, a semiconductor substrate, an optical material, a package, a thermal management system, and a radiation shield can be realized.
This microbattery technology may be compared to thin film battery technology but differs due to its use of Si as a structural component, a packaging component, and as a semiconductor to reduce weight, size, and cost (“Rechargeable thin-film lithium batteries,” Bates, et. al.,
Solid State Ionics,
70/71: 619-628 (1994); “Thin-film rechargeable lithium batteries,” Bates et. al.,
Journal of Power Sources,
54: 58-62 (1995); “Thin-film Li—LiMn
2
O
4
Batteries, ” Bates, et al.,
IEEE AESS Systems Magazine
, pp. 30-32 (April 1995)). In particular, previous thin-film microbatteries have not combined the use of Si wafers with advanced semiconductor packaging techniques so as to enable a highly functional integrated MEMS unit (“Development of Rechargeable Microbatteries for Autonomous MEMS Applications,” Salmon, et. al.,
Proc. Solid-State Sensor and Actuator Workshop
, pp. 338-341 (June 1998)). Preferably, microbattery fabrication leverages silicon technologies made in semiconductor processing over the past decade. Use of silicon technologies and the packaging techniques enabled thereby will decrease the cost and increase the functionality of integrated MEMS devices. In particular, resent development of several semiconductor fabrication processes has allowed the use of silicon substrates as structural foundation for autonomous, mesoscopic systems.
Perhaps the most important development has been a deep reactive ion etch (DRIE) process which has revolutionized the concept and implementation of mixed technology integration (“Method of Anisotrpically Etching Silicon,” Laermer, et. al., U.S. Pat. No. 5,501,893). Using the DRIE process, a Si substrate can be etched to specific depths with highly controlled lateral dimensions. This allows accurate alignment of dissimilar components and materials to one another and accurate wafer-to-wafer alignment. Utilizing on-chip microelectronic and mechanical structures, this technology will enable fabrication of a self-contained, highly versatile, integrated microsystem that will minimize volume, weight, and power requirements. DRIE also enables the pursuit of a collection of advanced packaging capabilities to address the need for complex microsystems that combine multiple materials and functions in a single package or assembly.
SUMMARY OF THE INVENTION
In one embodiment, a set of four Si wafers is used to form the planar microbattery structure. The two exterior Si wafers or frames are used to enclose and seal the anode and cathode of the microbattery while providing support for external circuitry. For example, on one Si frame, power management circuitry that is either pre-fabricated on the wafer, or attached as a hybrid, can be precisely located. The other exterior Si frame can be used to support photovoltaic cells that can be used as a power source for the microbattery. Through-frame plated vias can also be fabricated into the Si frame structures to provide electrical contact from the external circuitry to the anode and cathode. The interior Si wafers are patterned using DRIE in a honeycomb cell structure for placement of the anodic and cathodic battery materials. A patterned insulating layer overlaid by an electronic conductor can be placed onto the Si frames as one option for current collection. A dielectric porous membrane is located between the anode and cathode layers to prevent contact of the solid battery materials but allow the flow of the electrolyte material between electrodes as well as possibly providing continuous mechanical support throughout the structure. The silicon frames and interior electrodes are accurately aligned using alignment wells and pins. Bonding of the silicon frames can be used to form a hermetically sealed structure.
REFERENCES:
patent: 4087905 (1978-05-01), Cooper et al.
patent: 5338625 (1994-08-01), Bates et al.
patent: 5501893 (1996-03-01), Laermer et al.
Bates, et al, Rechargeable Thin-Film Lithium Batteries, 70/71; 619-628 (1994).
Bates, et al, Thin-Film Rechargeable Lithium Batteries, Journal of Power Sources, 58-62 (1995).
Bates, et al, IEEE AESS Systems Magazine, pp. 30-32 (Apr. 1995).
Solomon, et al, Proc. Solid-State Sensor and Actuator Workshop, pp. 338-341 (Jun. 1998).
Christenson Todd R.
Ingersoll David
Kravitz Stanley H.
Shul Randy J.
Zipperian Thomas E.
Bieg Kevin W.
Sandia Corporation
Yuan Dah-Wei
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