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Desiccant material refers to the material that can removing water and wet, such as calcium sulfate and calcium chloride hydrate forms; physical drying agent, such as silicon dioxide gel and activated alumina, dried by physically adsorbed water. Moisture control is the product yield is closely related to food, in the appropriate temperature and humidity, food bacteria and mold will be breeding at an alarming rate, the food spoilage, caused by moisture and color change. Electronics also due to high humidity caused by metal oxide, adversely. Desiccant is used in order to avoid the occurrence of excess water caused products defective.

Silicon dioxide properties:

In microelectronics, we use thin layers of pure SiO2. The layers are amorphous (fused silicon dioxide)

? Density: 2.0 - 2.3 gm/cm3

? Dielectric constant at low frequencies: εr = 3.9 (remember this!)

refractive index at optical wavelengths: n ≈ 1.5

? Breakdown field: > 107 V/cm (1 V across 1 nm)

? The interface with silicon always results in electronic trap levels and some negative interface charge. Typical interface defect density ≈ 1011 cm–2. This is not a high density of defects at an interface. It can be

made even lower by annealing in hydrogen.

The combination of the relatively good electrical properties of silicon, the excellent insulating properties of SiO2, and the low-defect interface between them is the key ingredient of modern integrated circuit electronics.

Oxidation of silicon:

There are several ways to form a layer of silicon dioxide on the surface of silicon.

The two pre-dominate methods are:

? Thermal oxidation of silicon - react silicon from the wafer with oxygen to create oxide.

? Deposition of a thin film by chemical vapor deposition.

(We’ll discuss this in detail later.)

Thermal oxidation is a simple process - introduce an oxidizing atmosphere to the surface of the silicon with sufficient temperature to make the oxidation rate practical. 

Typical oxide thicknesses range from a few nanometers to about 1 micron. The details of the process and a mathematical model are presented in the next lecture.



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