Application Note

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A PIN diode is a semiconductor device that operates as a variable resistor at RF and microwave frequencies. The resistance value of the PIN diode is determined only by the forward biased DC current. In switch and attenuator applications, the PIN diode should ideally control the RF signal level without introducing distortion which might change the shape of the RF signal. An important additional feature of the PIN diode is its ability to control large RF signals while using much smaller levels of DC excitation.

A model of a Microsemi PIN diode chip is shown in Figure 1. The chip is prepared by starting with a wafer of almost intrinsically pure silicon, having high resistivity and long lifetime. A P-region is then diffused into one diode surface and an Nregion is diffused into the other surface. The resulting intrinsic or Iregion thickness (W) is a function of the thickness of the original silicon wafer, while the area of the chip (A) depends upon how many small sections are defined from the original wafer. The performance of the PIN diode primarily depends on chip geometry and the nature of the semiconductor material in the finished diode, particularly in the I-region. Characteristics of Microsemi PIN diodes are controlled thickness Iregions having long carrier lifetimes and very high resistivity. These characteristics enhance the ability to control RF signals with a minimum of distortion while requiring low DC supply.

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•Application Note: PIN Diode Fundamentals