Evaluating Temperature Coefficient Wander in Thin Film Platinum Resistance Elements
Evaluating temperature coefficient wander in thin film platinum RTDs requires tracking substrate strain, glass passivation diffusion, and multi-point calibration.
Contact Metallization Drift
Electrical Interface
Deposition of thin metallic films onto a semiconductor substrate forms the electrical contacts required for signal extraction in integrated sensors. This critical interface is susceptible to contact metallization drift, which causes a gradual increase in contact resistance over the operating life of the device. Such change occurs when atoms diffuse across the boundary between the metal and the semiconductor.
Chemical Degradation
Interdiffusion of the metal atoms and the silicon substrate is accelerated at elevated operating temperatures. During contact metallization drift, the physical structure of the contact changes from a distinct boundary to a mixed intermetallic region. This alteration modifies the electrical characteristics of the junction.
Metrological Impact
Calibration parameters of the sensor degrade as the interface resistance fluctuates unpredictably. The contact metallization drift introduces a non-linear offset in the output voltage, which reduces the measurement accuracy. In ratiometric measurements, this drift can generate errors that exceed the specified tolerance limit of the instrument, necessitating frequent recalibration or sensor replacement.
Continuous monitoring of the contact resistance provides a method to track this phenomenon before it corrupts the primary data.
Mitigation Strategy
Incorporation of a diffusion barrier layer between the contact metal and the semiconductor material reduces the rate of atomic migration. Refractory metals such as titanium or tungsten are commonly employed for this purpose because of their high thermal stability. These barrier films prevent interdiffusion under typical operating conditions.