HfO2-Based Switching Devices with Nitridation of the Bottom Electrode
Authors: Misra Durga , Zeinati Aseel 
Published: February 2024

HfO2 -based Resistive Switching devices are a promising candidate for in-memory computing due to their low

power consumption, good endurance, reliability, and compatibility with CMOS technology [1]. Controlling the

oxygen vacancy (Vo) distribution near the top and bottom electrodes by selecting proper metal-dielectric-metal

stack materials has impact on the performance of the device [2-3]. Significant improvement in switching power

is 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 power

and 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 to

investigate its impact of BE TiN on the switching characteristics. Fig. 1 shows schematic for the two different

switching devices with identical top electrodes (10 nm PVD TiN) and same switching dielectric (10 nm HZO) but

with different N2 levels of 30 nm TiN at the BE. Device-B has higher level of N2 compared to device-A. Forming

process was performed by applying DC voltage sweep with 1nA compliance current. The device-A has the lowest

forming power (0.86nW) as shown in Fig. 2(a). An increase in the forming power consumption was observed for

device-B (2.45nW) as shown in Fig. 2(b). We carried out the carrier transport characterization at the high

resistance state (HRS) prior to forming process. Fig. 2(c)&(d) shows the conduction process in both devices. In

device-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 the

dielectric itself such as the trap energy level [6]. The conduction mechanism in device-B (high N2) (Fig. 2(d)) and

was dominated by the Schottky conduction in the HZO layer, which is an electrode-limited conduction that

depends on the electrical properties at the electrode-dielectric interface [6]. When the active nitrogen atoms are

introduced to the BE, it diffuses to the dielectric due to increased concentration, then connect to the hafnium ion

dangling 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 Vo

concentration near the BE for device-A leading to carrier hopping. On the other hand, Vo concentration near the

BE is completely purged because of high nitrogen concentration (device-B) leading to Schottky conduction. This

explains the reduction of forming power in device-A. Fig. 3 shows the resistance distribution after applying 30

DC sweeps with reading voltage of 0.1V after each sweep. The device-B (high N2) shows the largest window

between 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 window

between LRS and HRS because of Vo concentration variation near BE.

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Figure 1