An implantable hermetically sealed microelectronic device and method of manufacture are disclosed. Such barrier structure also protects the Cu or Al electrodes against oxidization during deposition of the high dielectric constant metal oxide. A utility function that is periodic in the frequencies of the lines in the spectrum is then computed. A reference strip with a plurality of reference emitters emit reference beams of different intensity, from which the processor selects an optimum emitter for compensating for drift.