What is the Young's modulus? The ratio of the normal stress to the corresponding normal strain in the elastic deformation stage of the material. In the elastic deformation stage of the material, its stress and strain are in direct proportional relationship (that is, it conforms to Hooke's law), and its proportionality coefficient is called the Young's modulus. "Young's modulus" is a physical quantity that describes the elasticity of a material. It is a general term, including "Young's modulus", "shear modulus", "bulk modulus", etc. Therefore, "Young's modulus" and "bulk modulus" are inclusive. Generally speaking, after an external force (called "stress") is applied to an elastomer, the elastic body will change its shape (called "strain"). The general definition of "Young's modulus" is: stress divided by strain. For example:

● Linear strain: A tensile force F is applied to a thin rod. This tensile force divided by the cross-sectional area S of the rod is called "linear stress". The elongation dL of the rod divided by the original length L is called "linear strain". Linear stress divided by linear strain equals Young's modulus E=(F/S)/(dL/L).

● Shear strain: When a lateral force f (usually friction) is applied to an elastic body, the elastic body will change from a square to a diamond. The angle a of this deformation is called "shear strain". The corresponding force f divided by the force area S is called "shear stress". Shear stress divided by shear strain equals shear modulus G=(f/S)/a.

● Volume strain: When an overall pressure p is applied to an elastic body, this pressure is called "volume stress". The volume reduction of the elastic body (-dV) divided by the original volume V is called "volume strain". Volume stress divided by volume strain equals volume modulus: K=P/(-dV/V). In order to avoid confusion, the Young's modulus of general metal materials refers to Young's modulus, that is, the positive Young's modulus. Unit: E (Young's Modulus) GPa.

The Young's Modulus of silicon (Si) material is related to its crystal orientation and purity. The following are common value ranges and descriptions:

1. Young's modulus of single crystal silicon

Single crystal silicon is anisotropic, and the Young's modulus of different crystal directions is different:

●<100>crystal direction: about 130–135 GPa

●<110>crystal direction: about 165–170 GPa

●<111>crystal direction: about 180–190 GPa

Description: Single crystal silicon is widely used in semiconductor devices. The anisotropy of its Young's modulus will affect the design of micro-electromechanical systems (MEMS) devices (such as cantilever beams and mechanical properties of thin film structures).

2. Young's modulus of polycrystalline silicon

Due to the random grain orientation, the Young's modulus of polycrystalline silicon is isotropic, with a typical value of about 160–169 GPa (close to the average value of the<110>crystal orientation of single crystal silicon). 3. Influencing factors Temperature: The Young's modulus decreases with increasing temperature. For example, the Young's modulus of silicon at room temperature (25°C) is about 169 GPa, while it may drop to about 160 GPa at 100°C. Doping: The effect of impurities (such as boron and phosphorus) on the Young's modulus is small and can usually be ignored (the change range is < 5%). Microstructure: The Young's modulus of nanocrystalline silicon or porous silicon will decrease significantly due to the increase in porosity (for example, porous silicon can be as low as 10–50 GPa).