As in the case of the iPhone 6S and later models, the iPhone X has the "3D Touch" function for sensing touch inputs. The 3D Touch distinguishes the force of a finger pressing the screen into three levels. Different functions are activated or different tasks are executed depending on the level of the force.
After tearing down the iPhone X, we found that Apple Inc had employed a new method for the pressure sensor of the 3D Touch. The method is different from the method employed for the previous models of the iPhone. Apple used a capacitive sensing method for the iPhone 8 Plus and older models but employed a resistance method for the iPhone X.
In other words, the company replaced the method of checking the capacitance change between the electrode of the pressure sensor and a finger with the method of checking the resistance change of the wiring pattern formed on the pressure sensor.
Pattern of sensing area changed depending on area
The resistance method features a high resolution of pressure sensing. It enables to distinguish the force of a finger pressing the screen into more than three levels. When an image of the iPhone X's pressure sensor is enlarged, patterns that are peculiar to the resistance method (e.g. spiral pattern) can be seen.