IC researchers integrate more than transistors

IC researchers integrate more than transistors
By Nicolas Mokhoff, EE Times
November 27, 2001 (12:59 p.m. EST)
URL: http://www.eetimes.com/story/OEG20011115S0074

MANHASSET, N.Y. — As microelectronics fabrication techniques allow more than transistors to occupy a piece of silicon, engineers are integrating components from the worlds of biology, chemistry and physics on chips as well. Technical papers that detail novel approaches to this continuing integration phenomenon will highlight next month's International Electron Devices meeting (IEDM) in Washington.

Researchers from the Microelectronics Institute (Athens, Greece), for example, will discuss enabling technologies for developing optical biochips whose results can be read without external optical components. The novel optical transducer consists of light sources, optical fibers and detectors that are monolithically integrated on an IC.

Unlike existing optical biochips that are made on quartz or glass slides and that require epifluorescence or confocal microscopy to read results, this chip requires only a standard electrical signal readout. This development heralds all sorts of possibilities for point-of-use determinations and real-time in vitro and in vivo multianalyte detection, according to the researchers.

Meanwhile, researchers at Duke University (Durham, N.C.) will discuss their Mist technology concept. This metal-insulator solution transport device is a potential enabling technology for high-throughput methods in synthetic and analytical chemistry and biochemistry that require rapid, automatic handling of minute quantities of liquids. The ultralow-power microfluidic device is applied in integrated biomicroelectrofluidic systems (Bio-MEFS).

According to the researchers, the device is the MEFS equivalent of a MOSFET. Like the MOSFET, the Mist exhibits bilateral transport of fluids rather than electrons, is electrically isolated, uses a gate electrode for charge-controlled transport, has a high threshold voltage and is a square-law device, the researchers say.

The presenters will detail a Mist device model with its characterization data, and show how when integrated, it can enable the development of large-scale biofluidic systems, such as reconfigurable biosensors or microchemical synthesizing. Simulations show that the Mist chip offers certain advantages over pressure-driven continuous flow technology: It has double the throughput, is 200 times smaller in size, and has microwatts power dissipation vs. Watts.

In a more esoteric strand, researchers from the Institute of Microelectronics of Singapore will discuss the technology behind the first microfabricated thermal reactor that can be integrated with other components on an unheated surface. Prior to this development, thermal cycling typically was performed on the entire substrate containing the reaction chamber, which produced a slow thermal response due to the large parasitic thermal mass.

Microfabricated thermal reactors are used to amplify nucleic acids in so-called miniaturized total analysis systems. A novel thermal isolation design has been implemented by etching thro ugh a thermally conductive silicon membrane to eliminate thermal crosstalk between reactor and substrate, and to reduce parasitic heat capacitance. The result of this achievement promises to integrate the microreactor with other components in the analysis systems, either on one chip or in a hybrid.

In the far-out realm of using microelectronics with molecular and neurobiology, an invited paper from the department of membrane and neurophysics at the Max Planck Institute for Biochemistry (Martinsreid, Germany) will detail work on linking semiconductors and living cells. This work may lead to sensor chips for pharmaceutical screening, to actuator chips for modulating molecular signals and cellular growth and to neuroelectronic devices for neurocomputation and neuroprosthetics.

One example of the work in neuroprosthetics used large identified neurons from a pond snail to build elementary neuroelectronic devices. A silicon micro-prosthesis chip was created that is able to record neural excitation on vol tage-gated ion channels inserted into cells on the chip. Signal recognition and amplification on the chip is used to capacitive stimulate a second disconnected neuron.