Niobium Oxide and Tantalum Capacitors: Quantum Effects in Charge Carrier Transport

Niob-oxidové a tantalové kondenzátory - kvantové efekty v transportu náboje

conference paper

Czech

The aim of this paper is to characterize the physical processes responsible for a quality of NbO and Ta capacitors. This method for assessment of defects in active region of NbO and Ta capacitors is based on evaluation of VA and noise characteristics and theirs temperature dependences. For the capacitor polarized in the normal mode, (with the NbO and Ta electrode positive), ohmic, Poole-Frenkel and tunneling are the dominant conduction mechanisms. Insulating layer in these components has 30 to 100 nm and then they belong to nanoscale electronic devices in which quantum effects play important role. The concentration of localized energy states in insulating layer Nd = 1018 to 1019 cm-3. For such doping concentration the impurity band is created with Eimp = 10 to 20 meV. To explain the ohmic current component electrons must be considered as waves with wavelength of the order of 1 nm. The conduction can occur by thermally activated hopping in impurity band and tunneling between deep impurity states. When an electron moves from one localized state to another it will exchange energy with a phonons. It may be expected that the mobility will have a thermally activated nature and its value will be at room temperature of the order of μ = 10-2 to 10-4 cm2/Vs. Tunneling current component is dominant for electric field higher than 100 MV/m in both NbO and Ta capacitors. In this quantum effect electron penetrate barrier as a wave and moves from localized donor state to conduction band. This component becomes dominant for 50 nm insulating layer thickness at 5 V. Comparison of both technologies is given to show that NbO and Ta capacitors have identical conductivity mechanisms. But for NbO capacitors a unique mechanism appears after dielectric breakdown. It causes a high resistance failure mode and limits the current bellow the capacitors thermal runaway point, which prevents capacitors burning, whereas filtering characteristics remain unchanged.

The aim of this paper is to characterize the physical processes responsible for a quality of NbO and Ta capacitors. This method for assessment of defects in active region of NbO and Ta capacitors is based on evaluation of VA and noise characteristics and theirs temperature dependences. For the capacitor polarized in the normal mode, (with the NbO and Ta electrode positive), ohmic, Poole-Frenkel and tunneling are the dominant conduction mechanisms. Insulating layer in these components has 30 to 100 nm and then they belong to nanoscale electronic devices in which quantum effects play important role. The concentration of localized energy states in insulating layer Nd = 1018 to 1019 cm-3. For such doping concentration the impurity band is created with Eimp = 10 to 20 meV. To explain the ohmic current component electrons must be considered as waves with wavelength of the order of 1 nm. The conduction can occur by thermally activated hopping in impurity band and tunneling between deep impurity states. When an electron moves from one localized state to another it will exchange energy with a phonons. It may be expected that the mobility will have a thermally activated nature and its value will be at room temperature of the order of μ = 10-2 to 10-4 cm2/Vs. Tunneling current component is dominant for electric field higher than 100 MV/m in both NbO and Ta capacitors. In this quantum effect electron penetrate barrier as a wave and moves from localized donor state to conduction band. This component becomes dominant for 50 nm insulating layer thickness at 5 V. Comparison of both technologies is given to show that NbO and Ta capacitors have identical conductivity mechanisms. But for NbO capacitors a unique mechanism appears after dielectric breakdown. It causes a high resistance failure mode and limits the current bellow the capacitors thermal runaway point, which prevents capacitors burning, whereas filtering characteristics remain unchanged.

Niobium Oxide, Tantalum Capacitors, Quantum Effects, Charge Carrier Transport

ŠIKULA, J.; SEDLÁKOVÁ, V.; HLÁVKA, J.; SITA, Z.; HÖSCHEL, P.; TACANO, M.

2006

1. 1. 2006

Electronic Components, Assemblies and Materials Association

Orlando, Florida

0-7908-0108-6

Proceedings CARTS USA 2006 - The 26th Symposium for Passive Components

421

427

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