MIM capacitors with various Al_2O_3 thicknesses for GaAs RFIC application

The impact of various thicknesses of Al2O3 metal-insulator-metal （MIM） capacitors on direct current and radio frequency （RF） characteristics is investigated. For 20 nm Al2O3, the fabricated capacitor exhibits a high capacitance density of 3850 pF/mm2 and acceptable voltage coefficients of capacitance of 681 ppm/V2 at 1 MHz. An outstanding VCC-a of 74 ppm/V2 at 1 MHz, resonance frequency of 8.2 GHz and Q factor of 41 at 2 GHz are obtained by 100 nm Al2O3 MIM capacitors. High-performance MIM capacitors using GaAs process and atomic layer deposition Al2O3 could be very promising candidates for GaAs RFIC applications.

Morphological and electrical properties of SrTiO3/TiO2/SrTiO3 sandwich structures prepared by plasma sputtering

SrTiO3（STO） and TiO2 are insulating materials with large dielectric constants and opposite signs of the quadratic coefficient of voltage（α）. Insertion of a TiO2 thin film between STO layers increases the linearity of the capacitance in response to an applied voltage, to meet the increasing demand of large-capacitance-density dynamic random access memory capacitors. Both STO and TiO2 suffer from the problem of high leakage current owing to their almost equivalent and low bandgap energies. To overcome this, the thickness of the thin TiO2 film sandwiched between the STO films was varied. A magnetron sputtering system equipped with radio frequency and direct current power supply was employed for depositing the thin films. Ti N was deposited as the top and bottom metal electrodes to form a metal–insulator metal（MIM） structure,which exhibited a very large linear capacitance density of 21 fF/um-2 that decreased by increasing the thickness of the TiO2 film. The leakage current decreased with an increase in the thickness of TiO2, and for a 27-nm-thick film, the measured leakage current was 2.0 × 10^-10 A. X-ray diffraction and Raman spectroscopy revealed that Ti N, STO, and TiO2 films are crystalline and TiO2 has a dominant anatese phase structure.

Experimental analysis of an MIM capacitor with a concave shield

A novel shielding scheme is developed by inserting a concave shield between a metal–insulator–metal （MIM）capacitor and the silicon substrate.Chip measurements reveal that the concave shield improves the quality factor by 11%at 11.8 GHz and 14%at 18.8 GHz compared with an unshielded MIM capacitor.It also alleviates the effect on shunt capacitance between the bottom plate of the MIM capacitor and the shield layer.Moreover,because the concave shields simplify substrate modeling,a simple circuit model of the MIM capacitor with concave shield is presented for radio frequency applications.