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

Hafnium dioxide (HfO 2 ) and aluminum oxide (Al 2 O 3 ) 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 HfO 2 resulted in a capacitance density of 2.73 fF/mm 2 , while that with 59 nm of ALD Al 2 O 3 resulted in a capacitance density of 1.55 fF/mm 2 . This capacitance density increased, when the temperature was increased from 25 to 150 o C. 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 150 o C, the breakdown voltage of both films decreased, while the leakage current increased. These results show that both ALD HfO 2 and Al 2 O 3 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.