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U401(美国Siliconix)是一种低噪声N沟道结型场效应对管,可用作检测极微弱宽频带电流的输入级放大元件。它用于膜片钳仪中,系统噪声仅为0.32pA(RMS,10kHz带宽,见本期第126页图4)。实验中,我们用热烙铁碰U401栅极2s,烙铁移去后,发现系统噪声从0.32pA增加到1.0pA,换上一只新的U401重复实验,结果再现上述情况,从而证实烙铁直接焊烫FET栅极引线(根部未用镊子夹),将使FET电流噪声急剧增大。根据噪声理论,FET噪声包括栅极漏电流I_g的噪声σ_1和高频热噪声σ_2,σ_2∝1/g_m,g_m为跨导,总噪声σ=(σ_1~2+σ_2~2)~(1/2)。以上U401噪声增加的物理机制可能是,栅极被烫使FET的P半导体区产生了局部热应力,导致了热载流子快速表面化,使得I_g的1/f噪声(它取决于器件表面状态)增加和g_m下降(σ_2增加)。这个过程McDonald(1970,IEEE Tran.ED-17,2:134)发现的雪崩应力使双极型晶体管β值下降机理相似。
U401 (Siliconix, USA) is a low-noise N-channel junction field effect transistor that can be used as an input stage amplification element to detect very weak wide-band currents. It is used in patch clamps with a system noise of only 0.32pA (RMS, 10kHz bandwidth, see Figure 4 on page 126 in this issue). In the experiment, we touched the gate of U401 with a hot iron for 2 seconds. After the iron was removed, we found that the system noise increased from 0.32pA to 1.0pA. After replacing with a new U401 repeat experiment, the above results were confirmed, FET gate lead (root without tweezers clip), will make the FET current noise increases dramatically. According to the noise theory, the FET noise includes the noise σ_1 of gate leakage current I_g and the high-frequency thermal noise σ_2, σ_2α1 / g_m and g_m are transconductance, and the total noise σ = (σ_1 ~ 2 + σ_2 ~ 2) 2). The above physical mechanism for increasing the U401 noise may be that the gate is hot enough to cause localized thermal stresses in the P-semiconductor region of the FET, resulting in rapid hot carrier surface heating, resulting in a 1 / f noise of I_g (which depends on the device surface state) Increase and g_m decrease (σ_2 increase). The avalanche stress discovered by McDonald (1970, IEEE Tran. ED-17,2: 134) in this process makes the bipolar transistor β-value reduction mechanism similar.