very dense magnetic sensor arrays for precision ... - NVE Corporation

they have poor temperature compensation and usuallyrequire the formation of some type of bridge by usingexternal components. Alternatively they can be connectedin series with one differential amplifier per sensor resistor.Half bridges take up more area on a chip but offertemperature compensation, as both resistors are at the sametemperature. Half bridges can be used as field gradientsensors if one of the resistors is some distance from theother. They can function as field sensors if one of theresistors is shielded from the applied field.Metal 2 withvias to Metal 1Metal 1 withvias to GMRMetal 1GMRelementsOutV +GndBiasFigure 4 shows a portion of an array of 16 GMR halfbridgeelements with 5 µm spacing. The elements are 1.5µm wide by 6 µm high with a similar size element abovethe center tap. The bottoms of the stripes are connected toa common ground connection and the tops of the halfbridges are connected to a current supply. The center tapsare connected to 16 separate pads on the die. A bias strappasses over the lower elements to provide a magnetic fieldto bias the elements.Figure 5. Four individual elements of a 16-element array ofGMR half-bridge sensors with 15 µm spacing. The firstelements are shown without metal 1 and metal 2 layersand without metal 1 layers for clarity.An example of a biosensor array is shown in Figure 6.This biosensor has twenty individual sensor elements in a4x5 matrix. The resistance of each element can beindividually measured.Metal 2 withvias to Metal 1Metal 1 withvias to GMRGMRelementsMetal 1V +OutBiasGndFigure 4. Part of a 16-element array of GMR half-bridgesensors with 5 µm spacing. The first three elementshave portions removed to show the three layers andtheir interconnections.Wider spacing between the elements can be achievedwhile retaining the directional sensitivity of narrow stripesby using serpentine resistors as the lower elements. Figure5 shows the layout for a wider 16-element array with 15 µmspacing. Serpentine resistors with 4 stripes are used for thelower sensor element, and a single, longer stripe for theupper element. For clarity of the interconnections betweenlayers, some of the elements are shown without metal 1 andmetal 2 layers.Figure 6. A biosensor array of 20 GMR elements arrangedin a 4x5 matrix.3