# Rapid and Cost-Effective Fabrication and Performance Evaluation of Force-Sensing Resistor Sensors
## 3 Results  
### Analysis of Piezoresistive Components in FSR Sensors  
An analysis was conducted to compare the components and composition that determine the piezoresistive properties of FSR sensors under load, utilizing a field emission scanning electron microscopy (FE-SEM, Hitachi S-4800 (Tokyo, Japan)) and an energy dispersive X-ray fluorescence (EDXRF, Horiba EX-250 (Kyoto, Japan)). Figure 4 presents the SEM images of the Flexiforce A201 FSR Series (Tekscan, Inc., Boston, MA, USA) and the Interlink FSR-402 (Camarillo, CA, USA). Table 1 provides an analysis of the chemical composition. The composition ratio of each sensor was measured twice.  
As shown in Table 2, the chemical composition of the FSR sensor is primarily based on the conductor carbon (C), with oxygen (O), silicon (Si), or tin (Sn) as additional components. Here, O is presumed to be a mixture of conductive and piezoresistive materials, while Si and Sn are considered to be the materials exhibiting piezoelectric properties under applied loads.  
The Flexiforce A201 Series (Flexiforce A201-1, Flexiforce A201-25, Flexiforce A201-100, Flexiforce A201-125) features the same piezoresistive area while differing in allowable load. The components influencing these differences in allowable load indicate that the composition ratio of O has a minimal effect, whereas the composition ratios of C and Si significantly impact the range of allowable loads. For the A201-25, compared to the A201-1, the composition is adjusted by reducing the weight ratio of the conductive material C to decrease conductivity while increasing the weight ratio of the piezoresistive material Si to enhance the piezoelectric effect.  
In terms of FSR sensor performance, it is inferred that appropriate adjustment of the composition ratios of conductive and piezoresistive materials can impact the allowable load and sensor linearity, assuming a uniform arrangement of constituent particles is achieved. Comparing the compositions of the Flexiforce A201 Series with the Interlink FSR-402 reveals that while C and O are consistent, the Interlink FSR-402 utilizes Sn as the piezoresistive material. Notably, the Interlink FSR-402 shows a nearly 1:1 composition  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Chemical** \\ **Composition (\%)** \\ \end{tabular} } & \multicolumn{2}{c}{**Flexiforce A201-1**} & \multicolumn{2}{c}{**Flexiforce A201-25**} & \multicolumn{2}{c}{**Interlink FSR-402**} \\ \cline{2-6}  & **1 st** & **2 nd** & **1 st** & **2 nd** & **1 st** & **2 nd** \\ \hline C & 55.23 & 59.33 & 42.71 & 46.24 & 41.21 & 39.39 \\ \hline O & 36.32 & 33.59 & 36.27 & 37.94 & 18.25 & 19.54 \\ \hline Si & 8.45 & 7.01 & 20.02 & 15.81 & & \\ \hline Sn & & & & & 40.53 & 41.08 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Chemical composition of the FSR sensors.  
Figure 4: SEM images of (**a**) Flexiforce A201-1, (**b**)Flexiforce A201-25, and (**c**) Interlink FSR-402.  
ratio of conductive material C to piezoresistive material Sn, and the composition ratio of O is approximately 15% lower than that in the Flexiforce A201 Series. This difference in piezoresistive materials between the Flexiforce A201-1 and the Interlink FSR-402 results in distinctly different output characteristics under load.  
Therefore, the output characteristics of the FSR sensor are determined by the composition ratio of the conductor C to the piezoresistive materials Si or Sn. Consequently, an FSR sensor was fabricated using C and Si, offering cost efficiency, easy accessibility, and rapid production.