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Matrix based on Magnetic Tunnel Junction (MTJ) and Diode Biochip
During 2006, INESC MN started developing a matrix based biochip where each cell consisted of a series of a thin film diode, and a magnetic tunnel junction. The advantage of this architecture is the direct scaling to large probe numbers. The first prototypes targeted 256 probes. Fig.3 shows the new matrix architecture.
Fig.3- MTJ+diode cell architecture for a 256 probe biosensor matrix.
Fig.4 shows the linear MTJ response (AlOx MTJs with amorphous CoFeB free layers with crossed anisotropies).
Fig.4-Transfer curve of the MTJ in the MTJ+diode cell.
Difficulties occurred with MTJ linearization and diode shorts. A fuse like element was introduced at each cell site, allowing taking away defective diodes or MTJs, and still leaving the matrix functional. Fig.5 shows the flow cell used over the matrix chip. The sealing is done via a PDMS o-ring. In this design, the chip is mounted in a disposable PCB.
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Fig.5- Fluidic chamber for the 256 probe matrix chip.