STJ Quick Start Guide v 2.01
April 1, 2021
Page 17
Fig 8: The BiasScan panel acquires and displays the STJ I-V curve. The cursors are used to set the zero-point and bias voltage.
Here are the typical settings used in our prior work with Tantalum STJ detectors:
•
Starting Offset = -500
µ
V
•
DAC Stepsize = 1
µ
V
•
Scan Points = 500 (a good balance between resolution and time required)
•
Wait Time = 50 ms
With the settings above, the scan starts at -500
µ
V and increments 1000 times by 1
µ
V, i.e. terminating at
+500
µ
V, and waiting 50 ms between each increment for the voltage to settle. Reducing the Wait Time
directly reduces the time required for the scan. In the past we typically reduced the Wait Time when
doing a ‘sanity check’ bias scan, and increased it when doing careful measurements.
•
Press the Start Scan button and wait for the run to complete. The run time depends primarily
on the number of Scan Points and the Wait Time.
By default, the green bias current plot is selected. Click and drag in the plot to quickly zoom. Click and
drag on any of the axes to quickly pan. Right-click and select “Full Scale” to zoom all the way out. To zoom
in on the red noise plot, first right-click and select “Zoom Reference”, then click and drag as before.
There are two vertical cursors in the plot. The blue cursor is used to set the STJ Zero, and the yellow
cursor is used to set the STJ Bias voltage, as described below.
SET STJ ZERO
Because of imperfections in ground connections, and the DAC and associated electronics, there is an
offset voltage associated with the DAC zero-point, i.e. when the DAC is set to 0V, the STJ detector may in
fact be biased with a few 10’s of micro-Volts. The inflection point in the characteristic STJ I-V curve is used
to find the actual DAC setting that corresponds to 0V at the STJ detector. Drag the blue cursor to the