The mobile computing (e.g., smart phone and tablet) markets benefit from smaller component form factors and lower power consumption. Because current platform solutions for smart phones and tablets rely on multiple packaged integrated circuits (ICs) mounted onto a circuit board, further scaling to smaller and more power efficient form factors is limited. For example, a smart phone today will include a separate power management IC (PMIC), radio frequency IC (RFIC), and WiFi/Bluetooth/GPS IC, in addition to a separate logic processor IC. System-on-Chip (SoC) architectures offer the advantage of scaling which cannot be matched by board-level component integration.
Besides transistors, passives such as capacitors and inductors are key components in PMICs and RFICs. In a PMIC, capacitors are employed as filters and charge storage elements in switching DC-DC convertors. In an RFIC, capacitors are used in DC blocking and matching network elements. Conventional on-chip metal-insulator-metal (MIM) capacitors today typically have a maximum rating of 1V and the insulator will irreversibly break down when stressed to higher voltages. In PMIC and RFIC applications, voltages in excess of 1V are not uncommon and because of limitations on the MIM dielectric thickness, some implementations connect multiple capacitors in series (e.g., four 1V rated MIM capacitors in serial coupled to permit 4V operation). However, series connecting MIMs requires multiple interconnect metal levels and a large capacitor area. As such, capacitors often occupy a significant proportion of the PMIC and RFIC. In some implementations, one third, or more, of the chip area may be occupied by capacitors.