An Introduction to the SensorBit 4-T Cell:

The SensorBit technology is based on a new type of sensor cell patented by the University of Texas at Austin, the inventor of which is one of the co-founders of the company. Coupled with additional patents filed by the company, this cell is utilized to design a sensitive, portable, and adaptable electronic nose


The sensor cell is referred to as a 4-Terminal, or 4-T, design because of the four electrically addressable points: Two contacts to the Silicon wafer and two contacts to the Organic layer. A cross-sectional drawing of the 4-T cell is shown in Figure 1. The manufacturing of this cell is done using standard CMOS techniques by our foundry partner for all of the steps except for the Organic layer deposition. The Organic material is applied by SensorBit using an InkJet deposition system. The use of the InkJet deposition allows for us to work with a wide variety of Organic layers and receptor additions after the wafers and die have been fabricated. Figure 2 shows a representative top-down optical image of the 4-T cell with the Organic layer in place. The die shown in Figure 2 has been packaged into a testable form by our Packaging House and can be loaded into a socket for measurement.


Cross-section representation

Figure 1. Cross-section representation of the SensorBit 4-T Cell.


The sensing element of this cell is an organic semiconductor treated with the appropriate receptor for the chemical of interest. Organic semiconductors are an ideal material for this purpose since receptors can be conveniently attached to this material. When the gaseous molecule of interest, also referred to as the analyte, binds to the receptor, a positive charge is trapped in the organic semiconductor. This trapped positive charge changes the current flow of a silicon field-effect transistor channel below the sensing element. The transistor is biased by circuitry so that the system response has a linear relationship with the volume of gas present, greatly simplifying chemical identification. A key advantage of the patented sensor cell is enhanced sensitivity and stability by virtue of the fact that the sensing current is not measured directly through the material that is modified by the sensing gas.


20100407-K Packaged

Figure 2 Top-down optical image of the 4-T cell with the Organic layer in place.


Each sensor in the array is treated with one of a variety of receptors, causing each sensor to respond electrically to a given vapor in a unique fashion. The combination of all signals produced by the sensor array generates a characteristic electronic signature for a given vapor. Unknown vapors are then identified by comparing the result to the electrical signature of known vapors. In this fashion, the sensor array can be trained to respond to a given set of vapors.


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