Dielectric Properties Investigation of Metal-Insulator-Metal (MIM) Capacitors

Abstract

This study presents the construction and dielectric properties investigation of atomic-layer-deposition Al₂O₃/TiO₂/HfO₂ dielectric-film-based metal-insulator-metal (MIM) capacitors. The influence of the dielectric layer material and thickness on the performance of MIM capacitors are also systematically investigated. The morphology and surface roughness of dielectric films for different materials and thicknesses are analyzed via atomic force microscopy (AFM). Among them, the 25 nm Al₂O₃-based dielectric capacitor exhibits superior comprehensive electrical performance, including a high capacitance density of 7.89 fF·µm^-2, desirable breakdown voltage and leakage current of about 12 V and 1.4 × 10^-10 A·cm^-2, and quadratic voltage coefficient of 303.6 ppm·V^-2. Simultaneously, the fabricated capacitor indicates desirable stability in terms of frequency and bias voltage (at 1 MHz), with the corresponding slight capacitance density variation of about 0.52 fF·µm^-2 and 0.25 fF·µm^-2. Furthermore, the mechanism of the variation in capacitance density and leakage current might be attributed to the Poole-Frenkel emission and charge-trapping effect of the high-k materials. All these results indicate potential applications in integrated passive devices.

Keywords: atomic layer deposition; electrical performance; energy storage; laser direct writing; metal–insulator–metal capacitors.

Figure 1

Schematic illustration of fabrication process of MIM capacitors. (a) PR spin-coating. (b) Laser direct writing. (c) Bottom electrode deposition by laser direct writing. (d) Dielectric layer deposition by ALD. (e) Secondary PR spin-coating. (f) Laser direct writing and top electrode exposure. (g) Top electrode deposition and PR removal.

Figure 2

(a) SEM image of the Al₂O₃-based MIM capacitor. (b) The cross-sectional SEM image of the MIM capacitor. (c) The 25 nm Al₂O₃ film thickness test results obtained by ellipsometry spectrometer: where Psi represents the amplitude ratio, and Delta represents the phase difference. (d) XPS survey spectra of the prepared Al₂O₃ film. High-resolution XPS spectra of (e) Al 2p, (f) O 1s.

Figure 3

AFM images of MIM capacitors deposited with 25 nm Al₂O₃, TiO₂, and HfO₂ dielectric material, respectively. (a) ALD deposition of Al₂O₃ dielectric material. (b) ALD deposition of TiO₂ dielectric material. (c) ALD deposition of HfO₂ dielectric material. (d) The linear contour fluctuations in the directions are indicated by the black, red, and blue lines in Figure 3a–c.

Figure 4

The relationship between leakage current density and applied voltage of manufactured MIM capacitors with different dielectric materials and thicknesses. (a) J-V characteristics of Al₂O₃ dielectric MIM capacitors. (b) J-V characteristics of TiO₂ dielectric MIM capacitors. (c) J-V characteristics of HfO₂ dielectric MIM capacitors.

Figure 5

C-Q and C-V characteristic curves of 12.10 nm, 24.72 nm, and 49.73 nm Al₂O₃ dielectric capacitors. (a–c) The C-Q characteristic curves of three thicknesses of dielectric capacitors, respectively. (d–f) The corresponding C-V characteristic curves of three thicknesses of dielectric capacitors at different frequencies.

Figure 6

C-Q and C-V characteristic curves of 25 nm Al₂O₃, TiO₂, and HfO₂ dielectric capacitors. (a–c) The C-Q characteristic curves of three kinds of 25 nm dielectric capacitors, respectively. (d–f) The corresponding C-V characteristic curves of three kinds of 25 nm dielectric capacitors at different frequencies.

Figure 7

Normalized capacitance as the function of bias voltage of 25 nm Al₂O₃ capacitors at 10⁴ Hz, 10⁵ Hz, and 10⁶ Hz, respectively.