Abstract: An inkjet printhead chip structure and a method of estimating the working life through the detection of any defect on the chip structure. The method includes laying a metallic layer such as a tantalum layer over the chip and then shaping the metallic layer into a protective layer circuit. A portion of the metal protective layer covers the heating elements embedded in the chip. In printing, the heating elements heat up the ink to produce jets of ink. However, a portion of the heat is transferred to the metal protective layer thereby raising its temperature. Heat on the metal protective layer combined with any strayed residual ink bubbles that impinge upon the surface of the metal protective layer causes the metal to age. Since resistance of the metal protective layer will increase proportionally to the amount of aging, a measurement of the resistance is capable of estimating how much longer a given chip is suitable for use.