Measurement of inter-strip resistance

Measurements by Alex Chilingarov, Lancaster University

Description of the measurement

The inter-strip resistance is measured by applying a voltage on one strip and measuring the potential on the adjacent strip on a biased sensor. However the DC pad is only accessible on every second strip due to layout constraints in the MCMD processing. This will limit the sensitivity of the measurement as described below.

Measuring dU0/dI0 as indicated in the figure below gives the value of the bias resistor Rb. Assuming that all three bias resistors are identical and that Rgnd is close to zero the interstrip resistance Ris can be calculated from U0 and U1. Rgnd is the resistace from the bias resistance to the instrument GND via the bias rail, which in practice is a few ohms. Hence the point of the bias rail where the bias resistor is connected will float up and disturb the measurement. The smallest Ris that can be measured before this effect becomes dominant is

Results of measurements on w14

The plot below shows the measured bias resistance values from dU0/dI0, where the values are compatible with the design values

The measurement of the Ris is dominated by the non-zero Rgnd as explained below. The plot below show the measured values vs. bias voltage, and the limit set on Ris is Ris > 250 MOhm. This value is significantly larger than two times the bias resistor value, which is connecting the two implants via the bias rail.

-- LarsEklund - 06 Apr 2009