1. Overview Time structure of leakage currents
Setup proposed by Mark Raymond
about 70 sensors measured
several different effects observed
news on vacuum effects
CMN module
by Marko Dragicevic
HEPHY, Vienna

2. A Quick Reminder
Sensor Stability Measurements by Mark Raymond, Tracker Week 02/04
The Basic Setup
AC - measurement

3. The Vienna Setup Source Measure Unit DC Power Supply Scope Metal Box
Sensor on conductive rubber
Needle
Low- Pass filter for HV
Source Measure Unit
DC Power Supply
Scope
Metal Box

4. Comparison Sensor ID 30211433739909 AC - measurement
residual system noise }
≈100nA
AC - measurement by M. Raymond

5. Single Sensors/Modules:
Tested Sensors
Complete Batches:
Delivered on :
Batch : 11 Sensors
Batch : 4 Sensors
Batch : 10 Sensors
Batch : 12 Sensors
Batch : 12Sensors
Delivered on :
Batch : 15 Sensors
Single Sensors/Modules:
Sensor
(bad one from IC)
Module
(CMN problem from UCSB)
Sensor
Sensor
Sensor
Sensor
70 sensors tested

6. Effects observed I { 400nA Increased Noise (@550V; 2,1µA)
Ripples 16,2µA)
several sensors found
at high HV (>500V) most sensors
2 sensors found so far
additionally some show ripples after rampup for a few s

7. decrease in noise corresponds to a decrease in DC current
Effects observed II
after a few seconds
Receding Noise 2µA)
Residual Noise 1,7µA)
decrease in noise corresponds to a decrease in DC current

8. time between measurements
Effects observed III
same sensor!
time between measurements
1 Day
Asym. Noise 0,5µA)
Noise Upwards 1µA)
Usually noise points "downwards" (= increased current)
Only sensor which points "upwards"

9. Most "bad" sensors show high current but:
AC – DC
Most "bad" sensors show high current but:
High noise at low current
1,1µA)
Low noise at increased current
2,5µA)
Tendency towards increased current but no direct linkage!

10. Remark: Vacuum Effect Voff - rampup rampdown - Von - ramup
rampdown - Voff - Von - rampup
rampdown - Voff - move sensor - Von - rampup

11. CMN Problem ModuleID: 30200020020516 - CMN Module from UCSB
CM- Corrected Noise measured with ARCS
UCSB
VIENNA

12. CMN Problem CMN module (@450V; 13,3µA) residual system noise
Zoomed View, red line depicts average system noise

13. "Bad" sensors so far improvement in the last batches seems eligible
Measured Batches:
Delivered on :
15 sensors tested - effects observed on 3 sensors*
Delivered on :
no Rint problem, final manufacturing process?
49 sensors tested - effects observed on 3 sensors*
improvement in the last batches seems eligible
*at bias voltages between V

14. Conclusion?
Outcome:
Correlation of noisy bias current and CMN problems seems eligible
remember: assumption based on just one tested module!
Low bias current does not exclude noise problems
Latest batches seem to have improved, but:
bad sensors can still be found
Screening is necessary, but:
used method is not entirely suitable (sensitivity, reliability,…)

15. Conclusion?
Problems:
no "easy" way to find bad sensors with a simple cut
no theory explaining all varieties of observed effects
validity of measured data over time:
IV – curve of some sensors is not always reproducible
observed effects may vanish or set in at higher bias voltage
Bad sensors may heal (a case easy to find)
but good sensors may fail (a case hard to find)
Zillertaler Alps, Tyrol - Austria

16. Sensor "Moods" No. 1 The Standard Type (most „good“ sensors):
Low current (I < 1.5µA) up to 400+V currents stable
≫400V high current after RampUp – causes high noise
Current decreases in a few seconds – noise recedes with „Overcurrent“

17. Sensor "Moods" No. 2 The Fear the Voltage Type:
Increase in voltage causes high current for a few seconds
At a certain voltage (around 400V) Ripples show up
Ripples decrease with current
Ripples turn into Noise when current is stable

18. Sensor "Moods" No. 3 The Fidget Type (Mark Raymond like Sensors):
Draws high current 400V)
Ripples already at low Voltage
Increase with Voltage
Instablities never recede

19. Changes over time Voltage needed to observe effect may change
DC current changes