HfO2-Based Switching Devices with Nitridation of the Bottom Electrode

Abstract

HfO2 -based Resistive Switching devices are a promising candidate for in-memory computing due to their lowpower consumption, good endurance, reliability, and compatibility with CMOS technology [1]. Controlling theoxygen vacancy (Vo) distribution near the top and bottom electrodes by selecting proper metal-dielectric-metalstack materials has impact on the performance of the device [2-3]. Significant improvement in switching poweris achieved when Vo distribution is higher near the top electrode (TE) and lower near the bottom electrode [4].Introducing nitridation treatment to the TiN bottom electrode shows a significant reduction in switching powerand superior conductance quantization with nanosecond pulse width of programing pulsed operation [5].In this work we studied different TiN bottom electrode (BE) films in the TiN/HZO/TiN MIM toinvestigate its impact of BE TiN on the switching characteristics. Fig. 1 shows schematic for the two differentswitching devices with identical top electrodes (10 nm PVD TiN) and same switching dielectric (10 nm HZO) butwith different N2 levels of 30 nm TiN at the BE. Device-B has higher level of N2 compared to device-A. Formingprocess was performed by applying DC voltage sweep with 1nA compliance current. The device-A has the lowestforming power (0.86nW) as shown in Fig. 2(a). An increase in the forming power consumption was observed fordevice-B (2.45nW) as shown in Fig. 2(b). We carried out the carrier transport characterization at the highresistance state (HRS) prior to forming process. Fig. 2(c)&(d) shows the conduction process in both devices. Indevice-A, the current conduction mechanism followed the hopping conduction in the dielectric as shown in Fig.2(c). The hopping conduction is a bulk-limited conduction mechanism depends on the electrical properties of thedielectric itself such as the trap energy level [6]. The conduction mechanism in device-B (high N2) (Fig. 2(d)) andwas dominated by the Schottky conduction in the HZO layer, which is an electrode-limited conduction thatdepends on the electrical properties at the electrode-dielectric interface [6]. When the active nitrogen atoms areintroduced to the BE, it diffuses to the dielectric due to increased concentration, then connect to the hafnium iondangling bonds as their lone-pair electrons, since the bonding energy of the Hf–N bond is very low (535eV)compared with that of the Hf–O bond (801eV) [7]. This allows a migration of Vo towards TE and reducing the Voconcentration near the BE for device-A leading to carrier hopping. On the other hand, Vo concentration near theBE is completely purged because of high nitrogen concentration (device-B) leading to Schottky conduction. Thisexplains the reduction of forming power in device-A. Fig. 3 shows the resistance distribution after applying 30DC sweeps with reading voltage of 0.1V after each sweep. The device-B (high N2) shows the largest windowbetween HRS and LRS compared to the other devices. That further confirms the forming process in these devices.In summary, low level of N2 reduces the forming power while higher level of N2 enhances the resistance windowbetween LRS and HRS because of Vo concentration variation near BE.