Donald E. Ackley

Electric field directed assembly of an InGaAs LED onto silicon circuitry

We demonstrate an electrophoretic process for assembling very small devices on a silicon circuit. A 20-/spl mu/m diameter InGaAs LED was fabricated and then released from the substrate by etching a sacrificial layer underneath the diode structure. The diode, placed into a buffer solution over the silicon circuit, was positioned onto the circuits tin/lead contact electrodes by biasing the contacts to establish an electrophoretic current in the buffer solution. Following removal from the buffer solution, the assembly was heated to reflow the solder. Circuit formation and LED activation is demonstrated by forward biasing the LED using the silicon circuits contacts.

A laminated, flex structure for electronic transport and hybridization of DNA

We have developed the first prototypes of a three-dimensional, electrophoretically driven microlaboratory for the analysis of proteins and DNA. By selecting the appropriate spacing and geometrical configuration, oligonucleotides were transported, in a controlled, rapid fashion, by electrophoresis in free-space. Transport efficiencies over 2 mm distances exceeded 70%. Electrodes of similar design were combined with an electronically addressed DNA hybridization chip to form a fully electrophoretic microlaboratory. In this instance, gold-plated copper electrodes were patterned on a 2 mil thick polyimide substrate. This polyimide layer was stiffened with 20 mil of polyimide to provide support for flip-chip bonding of our standard 100-site Nanochip. This composite structure illustrated three-dimensional transport of target oligonucleotides, through a via in the polyimide, along a series of electrodes and onto the diagnostic chip. Upon reaching the diagnostic chip, electronic hybridization was performed for a competitive reverse dot blot assay. The electronic assay showed a specific to nonspecific ratio in excess of 20:1. These results suggested that this type of structure might be of practical consequence with the development of a microlaboratory for biowarfare applications.

Two-dimensional LED arrays for virtual display image sources

The design and fabrication of large-scale two-dimensional (2-D) arrays of visible light emitting diodes (LEDs) is described along with their implementation as image sources for prototype virtual displays. The LED pixels were fabricated in the InGaAlP material system using a double mesa etch process. Pixel characteristics are presented and used to predict display luminance properties. The 10-/spl mu/m square LEDs produced external quantum efficiencies of 0.5% with an emission spectrum peaked near 650 nm (red). This performance level allowed the target display luminance of 10 fL to be attained with just 2.9 mW of array power consumption. The LED arrays consisted of 240 columns/spl times/144 rows (/spl sim/VGA/8) with pixels on a 20-/spl mu/m pitch and were driven in a column major matrix addressing mode at 60 frames per second for image display. Pixels were driven at a constant current with pulse width modulation to achieve sixteen levels of gray. An analysis of array luminance uniformity is presented. Sample images of text, graphics, and gray scale images demonstrate the capabilities of the LED arrays as monochrome image sources for virtual displays.

DNA technology for optoelectronics

High performance photonics systems and subsystems require increasing sophistication in packaging and assembly technology to achieve their performance targets. We are exploring DNA labelling techniques to achieve the precise placement of semiconductor structures on host substrates. These labelling techniques allow the electrophoretic transport of the semiconductor structures in solution, as well as the specific matching of structures to host locations due to the complementary base pairing inherent in DNA hybridization. By configuring an electrode array on the host substrate, various semiconductor structures may be manipulated in solution using the electric fields created by applying a potential to the electrodes. In conjunction with the inherent selectivity of the DNA base pairing (in a process known as hybridization) specific placement and orientation of the structures on the host substrate may be achieved.

Directed assembly of optoelectronic components using electric fields

We have demonstrated the directed assembly of objects ranging in size from 100 nm to 10 /spl mu/m onto electrode arrays fabricated on Si substrates. An example of this technology is shown. This experiment involves the manipulation of plastic beads of various sizes in solution over the chip.