| A team of researchers from the Instrumentation and Controls and Solid-State Divisions
have developed the first photo-spectrometer realized using only the materials, masks, and
fabrication steps inherent to a standard integrated circuit (IC) process. Since a standard
IC process is used, this photo-spectrometer can be realized on the same IC as powerful
analog, digital, and wireless circuitry. Thus, an instrument that now requires a
photodiode array and external optical filters, analog signal conditioning IC, digital
signal processing IC, and wireless transmission IC can be replaced with a single-chip.
Such a laboratory instrument-on-a-chip would expand the laboratory to include places like
groundwater, emergency medical care scenes, battlefields, and industrial process vessels.
Previous miniature photo-spectrometers all used expensive micromachining techniques. Thus,
mass production would require a large investment in new manufacturing infrastructure, and
devices would cost several hundred dollars each. The photo-spectrometer-on-a-chip,
however, is completely compatible with the existing commercial IC infrastructure, and
would cost less than $1 each to mass produce. A photograph of the new device, which
measures 2.2 mm X 2.2 mm X 0.5 mm, is shown in figure 1. This photo-spectrometer was
developed by taking advantage of mostly unused features of ICs. For example, different
depth diode junctions are used to separate long wavelength light from short wavelength
light, protective oxide coatings are used as thin-film interference filters, and
polycrystalline silicon coverings are used as wavelength sensitive absorption filters.
Since all of these structures and materials are part of the standard IC process, it cost
no more to use them to make spectrally sensitive electro-optical detectors than it does to
neglect their use in standard electronic circuits. Figure 2 shows the response of the
photo-spectrometer-on-a-chip to a gaussian input spectra centered at 500 nm (green). This
device is useful in the near ultra-violet, visible, and the near infrared regions, all of
which are important for chemical analysis, medical diagnostics, DNA sequencing, or color
imaging. This work was performed as part of the Optical Application Specific Integrated
Circuit (OASIC) LDRD. An invention disclosure describing this device was recently
submitted.
Figure 1. Photo-spectrometer-on-a-chip. |
Figure 2. The measured response of the photo- spectrometer-on-a-chip
to a gaussian input spectra. |
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