ALD HfO2 and Al2O3 as MIM Capacitor Dielectric for GaAs HBT Technology

Abstract

Hafnium dioxide (HfO2) and aluminum oxide (Al2O3) films have been deposited using atomic layer deposition (ALD) method and have been evaluated and used as metal-insulator-metal (MIM) capacitor dielectric in GaAs hetero-junction bipolar transistor (HBT) technology. The results show that the capacitor with 62 nm of ALD HfO2 resulted in a capacitance density of 2.73 fF/mm2, while that with 59 nm of ALD Al2O3 resulted in a capacitance density of 1.55 fF/mm2. This capacitance density increased, when the temperature was increased from 25 to 150oC. There was no significant change in capacitance density of these ALD films, when the applied voltage was varied from -5 to +5 V and when the frequency was increased from 1 kHz to 1 MHz. The breakdown voltage of the ALD hafnium dioxide and aluminum oxide films was measured to be at 34 V and 41 V, respectively. As the temperature was increased from 25 to 150oC, the breakdown voltage of both films decreased, while the leakage current increased. These results show that both ALD HfO2 and Al2O3 are compatible with, and suitable as MIM capacitor dielectric in GaAs HBT technology and can be adjusted to meet the specific application and requirements of the GaAs devices and designs.