An Ultra-Thin, Ultra-High Capacitance Density Tantalum Capacitor for 3D Packaging

Although embedded capacitors have been applied and researched for many years, their large-scale application still faces challenges such as low capacitance density, high thickness, high cost, and incompatibility with integrated processes. In this work, a breakthrough has been made in the fabrication of ultra-thin tantalum (Ta) capacitors with ultra-high capacitance density that can be used for 3D packaging. The key to these excellent performances is the application of Ta foil with nano-porous structure to the anode of the capacitor. The Ta foil with high specific surface area (SSA) is successfully prepared by direct current pulse etching. At a current density of 15 mA cm⁻², a pulse frequency of 50 Hz, and a duty cycle of 30%, the SSA of Ta foil is increased by 76 times after etching in an electrolyte with 0.01 v% TOA for 30 min. Based on this, Ta capacitors with a form factor of less than 40 µm, showing a capacitance density of 750 nF mm⁻² and a leakage current of less than 2.1 × 10⁻⁷ A at 8 V is successfully fabricated. To the best of the authors’ knowledge, this is the highest capacitance density reported to date for the mentioned form factors.