Conductive Mechanism of Bi-Doped Thick-Film Dielectric in High-Temperature Aging With Bias

The increase in high-temperature electronic applications is a challenge for the reliability of electronic packaging. Thick-film technology has the potential of operating at 300 °C. In a previous study of electrical reliability for multilayer thick films, bismuth (Bi) from the binder of a commonly used PtPdAu thick-film conductor diffused into the dielectrics during the multiple firing steps. If the dielectric was thin and the Bi was continuous through the dielectric, a significant increase in leakage current was observed between the two layers of conductor during 300 °C aging with bias. This paper studied the mechanism of leakage current increase in Bi-doped thick-film dielectrics. Two dielectrics,
$D1$
and
$D2$
, were intentionally doped with Bi in various weight concentrations. Capacitors fabricated with these Bi-doped dielectrics had a significant leakage current increase in a short time during aging at 300 °C with a 100-V bias in either polarity. Insulating substrate (sapphire) and conductive substrate (Pt foil) were used to replace the 96% Al
₂
O
₃
ceramic substrates to study the leakage current mechanism by separating the influences of leakage current and bias voltage (electric field). Doping Bi into the multilayer dielectric created traps during the firing process. Without leakage current, the traps were not activated during aging. When bias was applied to the top electrode, the electron flow through the dielectric activated the traps, resulting in the increase of leakage current. Traps created by doping with Bi in the thick-film dielectric,
$D1$
, were measured by ultraviolet and visible spectroscopy, and the trap energy was at 3.2–3.3 eV in
$D1$
with 3 wt% of doped Bi.