Patent ID: 8308066
Filing Date: 2012-11-13
Classification: B82Y,G01N,G06K

Abstract:
1. A method for encoding a thin film, comprising steps of: etching a semiconductor or insulator substrate to form a thin film including pores; varying etching conditions to vary porosity in the thin film according to a pattern that will generate an optical signature in the reflectivity spectrum in response to illumination, the optical signature including a grey scale code; wherein said step of varying comprises applying an etching waveform formed by the addition of at least two separate sine components in accordance with the following equations: wherein Equation (1) defines the amplitude of sine component n, which results in the spectral peak height, or grey scale of a bit; Equation (2) defines the frequency of the each sine component, which results in the spectral position of a peak, or identification of a bit (1st bit, 2nd bit, etc. . . );. Equation (3) defines sine component n, and Equation (4) defines the composite waveform used to drive the electrochemical etch.