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GaAsFFT 的特性分析中通常忽略了器件中信号沿栅宽方向传播所产生的影响。但是,当单个栅条的宽度很大时,这种传播的影响会使得器件的小信号增益出现不能接受的下降。用分布元件 FET 模型的计算预言:对于典型的 X 波段功率器件,当栅条宽度从150μm 增加到300μm 时,增益大约退化3dB。令人惊奇的是这一模型还预言一直到约为30GHz 的范围内,增益的退化实际上与频率无关。在本文中将要描述这一模型以及一些样品的计算结果。对于一直到约为30GHz 的频率范围内感兴趣的大多数栅宽可以采用一个增益退化因子的简单表达式。一旦知道了器件几何参数,有源层电阻率和栅金属层的电阻率,就可以迅速地用这一表达式计算任一 GaAsFET 器件结构的增益退化与栅宽之间的关系。通过在不同一 GaAs 片子上制作具有不同栅条宽度的 FET 检验了理论的预言。测量了这些器件在8～12GHz 下的小信号增益,发现随着栅条宽度的增加,增益下降的情况与计算结果相符甚好。
The characteristics of GaAsFFT are usually ignored in the device signal propagation along the gate width direction of the impact. However, the effect of this propagation can cause an unacceptable decrease in the small signal gain of the device when the width of a single gate is large. Computation Prediction with Distributed Element FET Model: For a typical X-band power device, the gain degenerates by about 3 dB as the grid width increases from 150 μm to 300 μm. Surprisingly, this model also predicts that, until about 30 GHz, the degradation of the gain is practically frequency independent. This article will describe the calculation of this model and some samples. For most gate widths of interest in the frequency range up to about 30 GHz, a simple expression of the gain degradation factor can be used. Once the geometry of the device is known, the resistivity of the active layer, and the resistivity of the gate metal layer, this expression can be used to quickly calculate the relationship between gain degradation and gate width for any GaAsFET device structure. Theoretical predictions were tested by fabricating FETs with different gate widths on different GaAs films. The small signal gain of these devices at 8 to 12 GHz was measured and found to be in good agreement with the calculated results as the gate width increases.