The realization of high density microfluidics in tandem with precise control of light on a chip has led to great anticipation of ‘lab-on-a-chip’ devices.  As part of several projects within the Optofluidic center, the addition of integrated active laser sources to the ‘lab-on-a-chip’ is proposed. In order to provide electrical and chemical isolation of the fluids from that of the host laser cavity material (typically active III-V semiconductor materials), a conformal passivation/isolation layer will be required.  We intend to use the conformal nature of plasma-enhanced chemical-vapor deposition (PECVD) to create a pure, high optical quality, silicon oxynitride (SiOxNy) “test tube” like environment for sample analysis within porous semiconductor photonic crystal based microresonators.  Additionally, we plan to exploit the well studied chemical interface properties of silica glass to promote intra-cavity binding of chemical or geometry specific species on the cavity walls.    

As an example, a proposed Quantum Cascade (QC) photonic crystal laser cavity test chamber for mid-IR spectroscopy is shown in Figure 1 (see the Optofluidic QC laser spectroscopy project).  The deep photonic crystal air holes etched into the semiconductor active region are to be coated with a conformal glass passivation layer, each hole thus providing a micron scale test tube.  The integration of the microfluidic and microcavity laser chips will also involve the sealing of a specially designed multi-level PDMS microfluidic chip with the surface of the semiconductor laser chip.  A series of different fluidic channels may be plumbed to each microcavity for different purposes, varying from sample delivery, to cleaning and wavelength trimming.  Above the microchannel fluid layer will be a control layer consisting of pneumatically actuated valves and pumps (a series of valves), and at the edge of the microlaser chip will be electrical contacts for addressing each microcavity laser.

Figure 1: Schematic of the cross-section of an integrated microfluidic and QC PC microlaser chip showing the "test chamber" of a single laser cavity.  Fluid containing the specimen to be analyzed is pumped through a microchannel fluid layer in the PDMS elastomer using pneumatically controlled valves in a top PDMS control layer. A fluid-tight seal between the semiconductor chip and the microfluidic chip is formed by a PDMS seal layer which conforms to a nearly planarized semiconductor surface. Once in the "test chamber", the fluid then fills the holes of the PC lattice bringing any biological or chemical samples it contains into the QC PC laser cavity.  A layer of silicon dioxide is used to coat the PC holes, providing a glass surface for sample containment and electrical isolation from the semiconductor. Electrical drive for the laser is provided by a buried metal layer which is run out to the periphery of the chip.  Fluid and pneumatic lines are run through tubes which are inserted into the top of the PDMS chip.

Research Group