Geometry optimization of TMR current sensors for on-chip IC testing

It was demonstrated that submicron and micron-sized tunnel magnetoresistive sensors having similar structure as magnetic random access memories can be used as very sensitive current sensors in μA-mA ranges, with a resolution of 5 μA. A number of variations in aspect ratio and dimensions, ranging from submicron to several microns, have been included in the design in order to investigate the influence of the sensor geometry on sensor properties. The influence of the shape anisotropy on the sensitivity is dominant over the current line width. Hysteresis investigations revealed that hysteresis of micron-sized sensors remains low and does not change significantly with the aspect ratio, while hysteresis of sensors with <2 μm rises drastically with decreasing shape anisotropy, especially aspect ratios close to 1. Invesigations of the temperature rise due to the Joule heating effect caused by the current under test also suggests that sensors of submicron size should be avoided to minimize sensitivity changes caused by the current heating effect.