Structure of thin-film lithium microbatteries

DETAILED DESCRIPTION The highest capacity thin film cathode layers (LiCoO.
sub.
2) typically require an annealing step of 700.
degree.
C.
Since this high temperature is not compatible with silicon device technology or flexible polymer substrates, the development of a low process temperature (<300.
degree.
C.
) cathode layer is needed.
LiCoO.
sub.
2 thin-films were RF sputter deposited and subsequently incorporated into thin film batteries.
A variety of deposition and post-deposition parameters were varied in an effort to optimize film microstructure and content.
Film composition and microstructure were examined using a variety of techniques including x-ray diffraction using synchrotron radiation.
It was found that LiCoO.
sub.
2 could be deposited at room temperature in a nano-crystalline state with a strong (104) out of plane texture and a high degree of lattice distortion.
By heating these layers to 300.
degree.
C.
, the grain size is significantly increased while lattice distortion is eliminated.
Cycling data reveals that the heating step increases cell capacity to near theoretical values (at lower discharge currents) while significantly improving both the rate capability and discharge voltage.
Accordingly, it is an object of the present invention to provide a thin film battery that has near-theoretical capacities and good discharge capabilities without exceeding temperatures of approximately 300.
degree.
C.
and are compatible with silicon processing techniques, which was heretofore a major problem.
Another object of the present invention is to provide a method for growing films with nano-crystalline grains oriented in the proper crystallographic direction at room temperature.
Yet another object of the present invention is to provide a simplified method for manufacturing thin-film batteries by heating the films to 300.
degree.
C.
in order to create cathode layers that have near state of the art performance.
These and other objects, which will become apparent as the invention is described in detail below, are provided by a process for making thin-film batteries including the steps of cleaning glass or a silicon substrate having an amorphous oxide layer several microns thick; defining with a mask the layer shape when depositing cobalt as an adhesion layer and platinum as a current collector; using the same mask as the preceding step to sputter deposit LiCoO