Ultra-tunable dielectric capacitors enhanced by coupling ferroelectric field effect and semiconductor field effect

Tunable ferroelectric film capacitors play an important role in tunable microwave devices and filter systems due to their high dielectric constant, low loss, and high dielectric tunability. However, there is a trade-off between low loss and high tunability, which limits further enhancement of dielectric performance. Here, we propose an ultra-tunable capacitor by designing a Ba0.7Sr0.3TiO3 (BST)–semiconductor heterostructure. In the tunable capacitor, the BST film is fabricated directly on p-type silicon substrates by magnetron sputtering, and a heterostructure layer is constructed. The coupling effects between the semiconductor depletion layer capacitance and the BST capacitance produce higher capacitance tunability than a traditional sandwich BST capacitor. Based on the coupling effects, a metal–ferroelectric–semiconductor–ferroelectric–metal capacitor is developed, which enables the capacitor to operate under both negative and positive biases, which has an n value (n=Cmax/Cmin) of 90 with 40 V bias voltage and a maximum Q of 1000. The results offer a potential approach to designing high-performance tunable capacitors on silicon with BST film that could build tunable filters for information processing in communication systems.