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Re: Power MOSET gate capacitance variations

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On 2017-12-25 11:40, Piotr Wyderski wrote:
> I've just measured ten MOSFETs from the same reel and their gate
> capacitance is between 1450 and 1900pF, with ~1620 being the most
> common. Since capacitance = area*permittivity/distance and the
> dielectric is the same SiO2, only area and distance (thickness) can
> vary. I don't think the manufacturer has no control over the area,
> as it is some form of litography, and thickness is proportional to
> the oxide growth time, which is exactly the same within a batch.
> So what is going on here?
>

Thicknesses and etching processes are not completely uniform across the 
whole wafer. This gets worse as companies move to larger wafers. You can 
guarantee ratios to be very close on the same device but not when 
compared with a device two inches from that location on the wafer.

Jim Thompson could shed more light on this.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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Thread

Power MOSET gate capacitance variations Piotr Wyderski <peter.pan@neverland.mil> - 2017-12-25 20:40 +0100
  Re: Power MOSET gate capacitance variations Joerg <news@analogconsultants.com> - 2017-12-25 12:08 -0800
    Re: Power MOSET gate capacitance variations Cursitor Doom <curd@notformail.com> - 2017-12-25 20:33 +0000
      Re: Power MOSET gate capacitance variations Joerg <news@analogconsultants.com> - 2017-12-25 12:41 -0800
    Re: Power MOSET gate capacitance variations Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-12-25 13:57 -0700
      Re: Power MOSET gate capacitance variations amdx <nojunk@knology.net> - 2017-12-26 07:48 -0600
  Re: Power MOSET gate capacitance variations Chris Jones <lugnut808@spam.yahoo.com> - 2017-12-26 23:10 +1100
    Re: Power MOSET gate capacitance variations "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-12-26 09:35 -0600
      Re: Power MOSET gate capacitance variations Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-12-26 14:57 -0500
      Re: Power MOSET gate capacitance variations Chris Jones <lugnut808@spam.yahoo.com> - 2017-12-27 22:48 +1100
    Re: Power MOSET gate capacitance variations Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-12-26 12:58 -0500
  Re: Power MOSET gate capacitance variations Winfield Hill <hill@rowland.harvard.edu> - 2017-12-27 05:32 -0800
    Re: Power MOSET gate capacitance variations Piotr Wyderski <peter.pan@neverland.mil> - 2017-12-27 16:15 +0100
      Re: Power MOSET gate capacitance variations Winfield Hill <hill@rowland.harvard.edu> - 2017-12-27 08:47 -0800
        Re: Power MOSET gate capacitance variations "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-12-27 11:47 -0600

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