Transconductance sensitivity enhancement in gated-MIS(p) tunnel diode by self-protective effective local thinning mechanism

Abstract

Gated-MIS tunnel diode with ultrathin oxide has been proposed as a transconductance device. The on/off current ratio of a device is sensitive to oxide thickness. For thicker oxide, the on/off current ratio and transconductance sensitivity are inferior due to the lower oxide tunneling rate. In this work, a technique of utilizing the effective local thinning effect created by positive voltage stress (PVS), which only occurs with the oxide thickness larger than about 3 nm, is demonstrated to improve the on/off current ratio and transconductance sensitivity. After PVS, the on/off current ratio and transconductance sensitivity are strongly enhanced by the creation of an effective local thinning at the edge of the MIS(p) tunnel diode. A transconductance of 8.5 × 10−7 S was found in gated-MIS(p) tunnel diode operated at VTD = 0.5 V and VG ≅ −0.12 V after PVS treatment in contract to that of 1.8 × 10−10 S before PVS.

Role of Schottky Barrier Height Modulation on the Reverse Bias Current Behavior of MIS(p) Tunnel Diodes

“…In [6][7][8][9][10], we can find that the reverse bias saturation current increases with oxide thickness. This phenomenon is believed to be caused by the Schottky barrier height modulating (SBHM) when a thin insulator layer is located between metal and semiconductor.…”

“…The term q(Vox-Vox0 ) in equation ( 8) indicates the Schottky barrier height modulation of MISTD. Then we adopt the tunneling probability by using WKB approximation [17] 𝑃 , (𝑉 , 𝐸′) = exp [− * ℏ ℰ ((𝑈 ) + (𝑈 − 𝑞𝑉 ) )], (9) where mox * =0.58 is the hole effective mass in oxide extracted by Fowler-Nordheim tunneling current [18], εox is the oxide field, and Ub is the oxide barrier height looking from metal by the hole. The dependency of Ub and E' can be written down as…”

“…Theoretically, Ub0 is 5.8eV. However, because of the nonuniformity of oxide [2,6,9], trap assist tunneling [19], and the existence of SiOx layer for about 5Å [2], a lower value of Ub0=4.3eV is adopted to fit the experimental result. Though 4.3eV is lower than the theoretical value, it still much higher than 3.1eV, which is the theoretical barrier seen by electrons when electrons tunnel from silicon to metal.…”

“…However, some studies of MISTD find that the current behavior is difficult to be described by [3][4][5]. For example, studies focus on deep depletion [6], fringing field [7][8], oxide nonuniformity [6,9],and carrier lifetime [10] all find increasing reverse bias current with oxide thickness. This phenomenon is difficult to be interpreted by [3][4][5].…”