Current through SiO2 gate oxide and its low frequency fluctuations: Trapping on charged dangling bonds with negative Hubbard U

Abstract

An estimate of Hubbard U supports instability of neutral one-electron Si dangling bonds in SiO2 and the formation of charged two-electron and two-hole negative U centers through the reaction Si•+Si•→Si++Si−••. The trapping on these negative U centers creates and annihilates “dents” in the thin barrier for electron and hole tunneling through the gate oxide. Such dents are visible as gate current low frequency fluctuations (1∕f noise). The longer trapping time of holes causes irreversible Si−••→Si+ conversion, which leads to stress-induced leakage current and accumulation of positive charge in the oxide under voltage stress.

Purely Electronic Switching with High Uniformity, Resistance Tunability, and Good Retention in Pt‐Dispersed SiO2 Thin Films for ReRAM

“…Incidentally, but not surprisingly, we also note that the negative‐ U centers have been studied in phase change memory materials that use similar chalcogenides 37. In addition to amorphous chalcogenides32, 37 and SiO 2 ,33, 34 negative‐ U centers have been studied in Si,35 doped GaAs,39 and other materials including ZnO,36 ZrO 2 /HfO 2 ,38 and perovskites 33, 40. In our material, mixing Pt and SiO 2 at the atomic level is expected to create many Pt/SiO 2 interfaces rich in dangling Si‐O bonds, which are known to host negative‐ U centers 33, 34, 39.…”

“…A prerequisite for such negative‐ U states is a strong electron–phonon interaction that leads to a sufficiently large local structural distortion, which occurs shortly after (over a time of 10 −13 to 10 −12 s) electron filling (happening in ≈10 −15 s) and lasts well within the residence time of the electron at the defect or center (ranging from 10 −9 to 10 −4 s) 33. Naturally, the need for easy structural distortions dictates that these centers tend to be situated near internal defects (e.g., vacancies)33–36 and surfaces (e.g., internal voids),33 and they are especially common in amorphous materials in which flexible (cation or anion) polyhedra and dangling bonds are commonplace 32–34. Indeed, the negative‐ U center was first proposed for amorphous chalcogenides because chalcogenides are relatively flexible and relatively covalent, thus accentuating the electron–phonon interactions 32.…”

“…In addition to amorphous chalcogenides32, 37 and SiO 2 ,33, 34 negative‐ U centers have been studied in Si,35 doped GaAs,39 and other materials including ZnO,36 ZrO 2 /HfO 2 ,38 and perovskites 33, 40. In our material, mixing Pt and SiO 2 at the atomic level is expected to create many Pt/SiO 2 interfaces rich in dangling Si‐O bonds, which are known to host negative‐ U centers 33, 34, 39. The Pt‐rich nanometallic pathways can then supply mobile electrons to these negative‐ U centers, and when two‐electron filling is made at a center, which occurs when the Fermi level is sufficiently lifted by V off to counter the internal bias caused by the work function differential between the electrodes, off‐switching (electron trapping or localization) takes place at the site.…”

Graded tunnelling barrier and oxygen concentration in thermally grown ultrathin SiOxgate oxide

“…This is by means of changing this built-in intrinsic transition. The channel carriers, which are penetrating into the gate oxide, are 'lost' for the channel conductivity and adversely affect the MOS reliability due to trapping inside the gate oxide [30]. Therefore it is better for the highest oxygen concentration to be at the SiO x -Si interface.…”

A study on Si/Al2O3 paramagnetic point defects

“…Such negative U centers are well known for SiO 2 gate oxides and SiN x and SiC films on Si. [22][23][24] Moreover, such double chargeable sites were suggested for oxygen interstitials in Si=Al 2 O 3 .…”