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# Method to Determine Substrate Potential And Chip Temperature

IP.com Disclosure Number: IPCOM000102861D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 38K

IBM

## Abstract

Forward bias voltage (V) and diode current (I) response of an FET diffusion region to temperature (T) and substrate potential (Vsx) is used to measure T and Vsx. Thus, T and Vsx can be measured by access to a single chip connection, e.g., an output enable pin of a mounted module, which is connected to a diffusion of a protect device on the chip.

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Method to Determine Substrate Potential And Chip Temperature

Forward bias voltage (V) and diode current (I) response of an
FET diffusion region to temperature (T) and substrate potential (Vsx)
is used to measure T and Vsx.  Thus, T and Vsx can be measured by
access to a single chip connection, e.g., an output enable pin of a
mounted module, which is connected to a diffusion of a protect device
on the chip.

For a grounded substrate, T of a diffusion in degrees Kelvin
is:
T = NqI/k(dI/dV)                        (1)
where N is the diode ideality factor, q is the charge of an electron,
k is Boltsmann's constant, I is the input current (for instance, 1
microamp), dV is the change in input voltage required to change the
input current (e.g., from 0.9 to 1.1 microamp) dI = 0.2 microamp.

If the substrate potential Vsx is not at ground potential, the
following expression for incremental current change Ii holds:
Ii=((dI/dV)/I)=C1/(T/295)(1+C2/(Vsx-V+C3)1/2)          (2) where C1,
C2, and C3 are constants typical of a given junction technology.  T
is in degrees Kelvin.  V and Vsx are magnitude values in volts.  Vsx
is found by measuring a first incremental current change Ii1 at one
value of input voltage V1 and a second incremental current change Ii2
around a second input voltage V2, then dividing Ii1 by Ii2. The value
of Vsx thus determined may then be substituted in equation (2) to
find the junction (and substrat...