Ferroelectric Dielectrics Integrated on Silicon

Chapter 8Integrated Capacitors ¹

 

 

 

8.1. Introduction

The integrated capacitors, apart from the tunable capacitors, are separated into two distinct families: the radio-frequency (RF) capacitors and the decoupling capacitors.

The RF capacitors are incorporated into a circuit that requires a very precise capacitance value, not necessarily large, and with very little variation in temperature and the polarization voltage. The perovskites can hardly be a solution for this application as the value of the permittivity varies with the polarization voltage and temperature. In addition, for values of capacitors in the pF range, the required perovskite surface is very small. Typically, for a value of 1 pF, the surface of a 100 nm thick BST capacitor with a relative dielectric constant of 400 is 5 × 5 μm². A simple lithography nominal error (typically 0.5 μm for MEMS) induces a capacitance uncertainty of around ±20%, which is most of the time not acceptable. However, there is an interesting perspective for this application: increasing the capacitance density (often in nF/mm²). Indeed, the standard capacitance density of the microelectronic industry for metal–insulator–metal (MIM) industry is between 2 nF/mm² and 5 nF/mm². The typical SiO₂ value is 2 nF/mm². With other dielectrics such as Ta₂O₅, a value of 5 nF/mm² can be reached. But to get higher values, we can consider the combination of very high permittivity dielectrics with highly linear dielectrics. A combination example of SrTiO ...