majormajor
Newbie level 5
A few weeks ago I grabbed some CD4007 chips as I was curious about the characteristics of the MOSFETs contained in the chip. As it is an ancient and very simple chip, I thought I'd educate myself and see how the individual transistors would measure. Taking into account that both the NMOS and PMOS transistors are on the same piece of silicon, I was wondering how similar they were.
I measured some very basic things, such as transconductance and output resistance, with the MOSFETs biased to 1 mA drain current. I had various devices from different decades (1990's, 2000 and current).
So the NMOS and PMOS devices turned out to be fairly similar; the threshold voltages and transfer characteristics looked almost identical (for example, transconductance at Id = 1 mA: NMOS was 1.6 mA/V, PMOS 1.5 mA/V), etc. All very nice and symmetrical. However, the output resistance is very different: about 160 kOhm for the NMOS and 16 kOhm for the PMOS. I must admit I didn't expect that. That's a factor of 10 difference. All devices showed the same behaviour.
So excuse my ignorance (I don't design chips for a living) but why? I'd be interested to know. What physical property of the chip accounts for this massive difference?
I measured some very basic things, such as transconductance and output resistance, with the MOSFETs biased to 1 mA drain current. I had various devices from different decades (1990's, 2000 and current).
So the NMOS and PMOS devices turned out to be fairly similar; the threshold voltages and transfer characteristics looked almost identical (for example, transconductance at Id = 1 mA: NMOS was 1.6 mA/V, PMOS 1.5 mA/V), etc. All very nice and symmetrical. However, the output resistance is very different: about 160 kOhm for the NMOS and 16 kOhm for the PMOS. I must admit I didn't expect that. That's a factor of 10 difference. All devices showed the same behaviour.
So excuse my ignorance (I don't design chips for a living) but why? I'd be interested to know. What physical property of the chip accounts for this massive difference?