9103 Picoammeter bias modes

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9103 Picoammeter bias modes

This post explains the 9103 picoammeter bias modes and also explains the concept of “floating”.

There are 4 picoammeter bias modes:

No bias – the current source is connected directly to the picoammeter input

No_bias_functionality

Internal – a low noise DC supply (two 45 V DC batteries in series) provides a bias between the current source and the input of the picoammeter. This application is typically used for providing a +90V bias to a target in a vacuum chamber in order to prevent secondary electrons from leaving the sample. Adding the 90V bias results in a more accurate measurement for both electron and ion current. It is also possible to use regular 9V batteries and so lower internal bias voltages are possible. Batteries are used for the internal bias as they are very clean with no ripple.

Internal_bias_functionality

 

 

 

 

 

External –

There are two external bias options for the 9103, both are limited to 600 V DC.

9103EXTBIASPR has a BNC connector on the back of the 9103 that connects to the customer’s voltage source which needs to be isolated from ground (floating).

9103DBPR (shown below) has two BNC connectors on the front panel of the 9103 and the 9103 floats on the customer’s ground referenced DC voltage source. 

The 9103DBPR is the most common external bias option as most voltage sources are referenced to ground (not isolated).

Two BNC connectors are used to float the 9103 up to as much as +/- 600V DC with an external low noise voltage source (provided be the user).    The voltage source is connected to the HV (signal ground) BNC connector and the 9103 and the current source (DUT) is connected to the Input BNC connector.

The maximum voltage that can be applied in this mode is 600V DC (that is the rating of the BNC input on the 9103 USB picoammeter).

external bias

External Bias Dual BNC

Floating – In this mode the picoammeter signal ground is raised from near chassis ground up to a value as high as +/- 5000V DC.   If you were to measure between the signal input and the signal ground reference the voltage would be low (under 1V typically). However measuring the DC voltage from the signal reference to chassis ground the voltage would be high, the floating supply value.

When floating the 9103 USB picoammeter there are some safety considerations. First of all, the input to the 9103 is changed from a BNC to either a SHV or MHV connector (user specified). These connectors are rated for up to 5kV. The recorder output on the back of the 9103 also floats. For example if you apply a floating voltage of 1000V the recorder output would also measure 1000V with respect to chassis ground. So if you are using the recorder output and also floating the 9103 the meter that you are measuring the recorder output with also needs to be isolated from ground. Finally, to prevent voltage spikes a current limit resistor is placed between the floating supply and the 9103 signal ground.   The floating mode is typically used to measure the collector output of an electron multiplier or a Faraday cup.

The maximum float voltage with the latest rev 9103 is +/- 5000 V DC.   If your 9103 was purchased before January 2019 then it can only float up to 1500V DC maximum.

The floating mode cannot be used with either the internal or external bias modes.  However you really would not need either of those options as you can float the 9103 up to get what ever bias you need.  For example,  let’s say you want to measure an ion beam that is at 3000V DC and you wanted to retard the ions by 200V.  You could simple set the bias supply to +3200 V DC and you would  be retarding the 3000 V beam by 200V DC.

For all modes of operation the chassis ground of the 9103 USB picoammeter should be connected to the ground on the PC or chamber.

If you would like more detailed information please contact us via email at the link in the upper right hand corner of our website at www rbdinstruments dot com.

Calibrating the SIMSII RF Generator

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Calibrating the SIMSII RF Generator

This post shows you how to calibrate the Balzers QMH RF generators that are used on the PHI SIMSII and 6300/6600 series SIMS systems.

1. Load in a Molybdenum sample. Note that the sample mount covers on PHI sample mounts are made out of Molybdenum so if you have one of those on your sample you can use the cover.

2. Monitor the voltage on the two recessed banana jacks on the front of the RF generator with a DVM set to DC millivolts.

tuning_test_points

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.  In AugerScan set up a SIMS alignment with a Peak AMU of 10 and a range of zero.  Note that for this adjustment the ion beam does not need to be on.

sims_alignment_dialog_box

 

 

 

 

 

 

 

 

 

4. Acquire the alignment and adjust the Tuning capacitor on the back side of the RF generator for the minimum voltage.   The capacitor is a tuning type like what was used in old radios. The shaft of the capacitor is attached to a wheel with holes in it. To adjust the capacitor you put a small thin screwdriver or an Allen wrench into one of the holes and move the capacitor wheel left and right. There is a little bit of hysteresis in the adjustment so you will need to go back and forth a little bit to make sure that you are at the minimum voltage value.

The DC voltage will minimize at about 10 to 20mV depending on the RF generator AM range and the size of the quadrupole.

Once you have minimized the DC voltage stop the alignment. Change the AMU to 50 and repeat step 4.

5. Next change the AMU in the alignment to 200 AMU and adjust for minimum voltage. 200 AMU is as high as you will need to go as most of the RF generators only go up to a maximum of 250 AMU. But even if you have one that goes up to 500 or even 1000AMU, the effective signal above 200 AMU is minimal and so I think that it makes more sense to optimize the tuning over the effective range of the RF generator rather than the absolute maximum AMU.    The voltage at 200 amu will be about 400 to 600mV depending RF generator AMU range and the quad diameter.  The important thing is to minimize the voltage at 200 AMU.

After tuning the next step will be to adjust the peak positions.

6. The ion beam needs to be set up for normal operation and the raster turned OFF. Open the O2 leak valve on the SIMS II energy analyzer (top of SIMSII) and set it so that the vacuum in the chamber is 2 X 10-7 Torr. There is some hysteresis in the gas line so be very careful when adjusting this valve. My technique is to slowly open the valve and as soon as I see the pressure in the chamber starting to come up I close the valve ¼ turn and wait for the pressure to stabilize before further adjustment.

7. Set up an alignment in POS SIMS with an AMU of 16 and a range of 3. Set the time per step to 50ms.

sims_adjustment_pots

 8. Acquire the alignment and adjust the Cal LOW potentiometer on the RF generator so that the 16 AMU O2 peak is centered. Note that for this adjustment the ion beam needs to be on. CCW moves peak up.

9. Change the AMU to 98 and a range of 3.   Adjust the Cal HIGH potentiometer on the RF generator so that the 98 AMU moly peak is centered. The 98 Moly peak will be the highest peak in the group of peaks between 92 and 100 AMU.  CCW moves peak up.

10. Recheck the 16 AMU peak and readjust if necessary. If you adjust the 16 AMU peak then you will also need to adjust the 98 AMU peak as well.

Next we will adjust the resolution linearity. The resolution is adjusted by a combination of the Resolution number in the software and also the actual resolution fine potentiometer on the RF generator. We will adjust the resolution for what is called the 10% value. The 10% value represents the ratio between the 95 and 96 Moly peaks and when viewed in the log scale is one order of magnitude on the graph. We further will want to adjust the resolution linearity so that the peaks from 90 to 100 AMU and also 185 to 195 AMU on Moly are both showing approximately a 10% peak to valley ratio, as shown in the survey below.

10_percent_linearity

The resolution number in the software acts like a resolution offset – it affects the entire range of AMU. The resolution gain potentiometer on the RF generator acts like a gain, it has more effect on the high AMU than the low AMU. By selecting the correct Resolution number in the software and adjusting the resolution Fine potentiometer on the RF generator the overall resolution linearity can be adjusted.

11. Set up two survey windows in AugerScan. One will be set from 90 to 100 AMU and the other from 185 to 195 AMU. Initially set the resolution in the software to the last known good value or the value that is written on the front of the RF generator. Use an AMU of .05 and a time per step of 50 ms, one sweep.

10 percent moly peaks

 

 

 

12. Acquire both surveys (one at a time).

In each window the goal is to have approximately 10% peak to valley ratio (in the log scale). Adjust the resolution number for the 90 to 100 AMU peaks and the resolution fine for the 185 to 195 peaks. CW = more resolution. Remember that the Resolution number in the software will affect both the low and high peaks, and that the resolution fine pot on the RF generator will have more effect on the high peaks than the low peaks. Here is a table that might be helpful-

sims_adjustment_table

 Note that any time you change the resolution number for the 90 to 100 survey you need to change it to the same value for the 185 to 195 survey.

After a few iterations you will have the resolution set so that both the low and high AMUs are approximately 10% resolution.

13. Once the resolution linearity adjustment is complete, recheck the 16 AMU and 98 AMU peak positions and adjust if necessary.

If you run out of range on the resolution fine adjustment or the cal low peak position contact RBD Instruments for additional procedures on how to correct those issues.

DGC IV calibration

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Years ago RBD Instruments had our DGC IV manufactured by JC Controls.  The DGC IV is basically the same thing as a IG4500.
Although we no longer produce the DGC IV, there are still a few of them in the field.  The calibration procedure is listed below.

 POTENTIOMETERS LIST

PR7(VREF)Reference Voltage Adjust                                                          Direction are with the front

PR4(TC1 Z)TC1 Zero Adjust                                                             of the IG4500 facing you.

PR6(TC2 Z)TC2 Zero Adjust                                                                            N

PR3            TC1 Gain Adjust                                                                                    W –+– E

PR5            TC2 Gain Adjust                                                                                         S

R1(EMIS)    Emission Adjust

PR2(ELEC)Electrometer Adjust

 

Power Supply Tests ( Ground)

  1. Attach Tester box to controller and check voltages on computer or do steps B,C,D,E
  2. Test -15,+15,+5 from 8 Pin Power Connector Pins   2,3,4.
  3. Turn on Ion Gauge
  4. Test +180 V From Grid Pin (Outside) of tube to Ground.
  5. Test +150 V from Grid Pin to Fil Pin (Outside to Inside) of tube.
  6. Check Degas

(1) Reference Voltage Adjustment

  1. Connect DC DVM from R14{E} to ground R31{E}
  2. Turn on IG4500 while holding down the SELECT switch,.
  3. While holding down the SELECT Switch, adjust PR7 (VREF) until the DC voltage is 10.000 ( +/- .001 )
  4. Release Select Switch and Check off Recorder output box
  5. Turn Power off and on, check that all the LED light up, if so check off Digit(LED) Test

(2) TC1 & TC2 Zero Adjustment

  1. Connect TC Cable to TC1 Input on back of IG4500.
  2. Connect a TC tube that is at Atmosphere to the cable.
  3. Connect DC DVM from R26{E} to ground (R31{E})
  4. Adjust PR4(TC1 Z) until DC Voltage is .133 VDC. (+/- .005 )
  5. Do the same with TC2, Using TC2 Input, R33{E} & PR6(TC2 Z).

(3) TC1 & TC2 Gain Adjustment

  1. Connect TC Cable to TC1 Input on Back of IG4500.
  2. Adjust PR3 through the back panel until the main display is the same vacuum as the Test Tube. Because TC Tubes work by Heat, give the tubes time to readjust after the pot is turned.
  3. Do then same with TC2, Using TC2 Input, Bar Graph & PR5.

 

(4) Emission Adjustment

  1. Use tester box or connect a current meter in series with Pin 3 of J1 ( Power Connector ).
  2. Connect IG cable to unit and a IG Test Tube. Connect the current source to the BNC on the unit.
  3. Turn on power and turn on ion gauge tube. Use current source to get to 10 mA range
  4. Adjust PR1 (EMIS) until you get 10.0 mA (+/- .05) on current meter.
  5. Use current source to switch down to 1 mA range, emission should be 1.00mA on current meter, Record current.

(5) Electrometer Adjustment

A. Connect current source to IG4500, set to 1uA. Turn on Ion Gauge.

B. Adjust PR2 (ELEC) so IG4500 displays 1.0-04.

C. Repeat Step B for 1nA=1.0-08, 100pA=1.0-09.

D. Also record for 10pA, it should be 1.0-10. (+/- 2.0)

 

(6) Setpoint & EEPROM

A. Check that the relay turn on and off by listening for them to click

B. Use the computer to set the serial number.

C. Turn unit off and on, Check serial number in “Edit Window” by entering =R#

 

Technical Modes of IG4500

* Enable Adjust Mode

This mode is for turning the System Enables on and off. It is entered by pressing and holding down the [ION] & [SELECT] buttons while turning on the main power . The display will show The Enable Name followed by either On or Off.

IGS Enables

Enable Name Description
F Filament Enable ( Display Mode )
Fd Full Duplex RS-232 Communication
C1 Code 1 enabled – Filament Overdrive
C2 Code 2 enabled – Under Vacuum, No Collector
C3 Code 3 enabled – Over Vacuum
A Averaging Enabled
E Emission Ranging Enabled

 

To Adjust the enables press the [ION] switch to select the different enables and the [DEGAS] switch to change from on to off. The Default for the IG4500 is All enables on.

** Timer and Control Mode

This Mode displays the timer value from the electrometer circuit. The value is a 6 digit Hexadecimal number. To put it on the 5 digit display either the lower 5 or the upper 5 digits will be displayed depending on if the high digit is a 0 or not. The Units LED’s are used as status LED’s

 

Display Unit LED’s

LED Name Status
Torr 25’th Bit of timer
Min Averaging On
mA Full Emission On

 

Mode 8 is entered by turning the Display switch to Emis. , then press the [ION] & [DEGAS] at the same time. The [ION] button will turn the Averaging on & off, you should make sure Averaging is disabled before adjusting it manually or else the controller will probably switch it back. The [DEGAS] button will switch between Full and 1/10 Emission Current.