Resistive Random-Access Memory (ReRAM) has gained significant attention as a promising non-volatile memory (NVM) technology due to its programmable nature and potential for high-density storage. These devices require an activation process called electroforming, which creates a conductive filament (CF) inside the insulator layer of the metal-insulator-metal structure. Under the influence of an external voltage, the CF forms and ruptures, leading to two stable resistance states: the high-resistance state (HRS) and the low-resistance state (LRS). A ruptured CF places the device in the HRS, while a formed CF results in the LRS. These two resistance states represent the binary "0" and "1" for encoding and storing information. Significant efforts have focused on improving key performance factors, such as the on/off ratio, which represents the resistance ratio between the low-resistance state (LRS) and the high-resistance state (HRS). In this work, the on/off ratio was evaluated in HfO2-based ReRAM devices consisting of TiN(30nm)/HfO2(5nm)/Hf(10nm)/TiN(30nm) stacks. The analysis was performed on samples with various areas: 55x55 nm², 65x65 nm², 75x75 nm², 85x85 nm², 105x105 nm², and 135x135 nm² (nm-scale), as well as 1x1 µm², 3x3 µm², and 5x5 µm² (µm-scale). All samples were electroformed with a compliance current of 5 mA, and their current-voltage (I-V) characteristics were measured under a DC voltage sweep at room temperature (Fig. 1). The on/off ratio was evaluated over more than 50 cycles for each sample during the set and reset processes. This ratio is defined by the relationship between the electrical resistance of the LRS and HRS, or by the relationship between the currents in the LRS and HRS near Vset during the set process and near Vreset during the reset process (Fig. 2). The on/off ratio was determined cycle by cycle to assess the variability. The mean value and variance are presented in Fig. 3. The fact that the on/off ratio is one order of magnitude higher in smaller devices suggests that the resistive switching (RS) effect is enhanced with scalability. This confirms that HfO2-based ReRAM devices at the nanoscale could be a promising option for high-density storage-class memory architectures. However, it is important to consider that variability tends to have a greater impact on smaller samples.