Cecile3rdDippingAt4K

3rd dipping at 4K (the right one?)

Tests at Room Temperature

2T Measurements

Use of the sensitive power supply : 3mV, 10 nA max

4-6 : 2,2 nA

4-12 : 2,2 nA

4-13 : 2,8nA

4-18 : 3,5 nA

4-16 : 3,6 nA

Leakage current

4-10 : 2,8 nA

R2T (4-6) = 1,36 MOhms

4T Measurements

Use of the AC Lock-in Amplifier :

Excitation 17Hz 500 MicroVolts

Gate ungrounded

13 - 16 : 120 (In) -7 (Out)

12 - 8 : 121 (In) -7 (Out)

12 - 13 : 1 (In) 0 (Out)

8 - 16 : 7 (In) 0 (Out)

All results in micro Volts.

Intensity through the Hall Bar : 6,5 nA

R4T = 18,5 kOhms

RF Resonance

• What is the RF power input?-- AlexHamilton - 20 Apr 2010

Resonance at 4K - 09/04/2010

Resonance_at_4K.txt

The resonance had shifted during the night, it is now less important 335MHz (more similar to what Lasse and Ben got) at 0 gate voltage. And it is now possible to match the resistance by changing the gate voltage.(RF Power : -30dBm)

• Cecile - you should put the FILENAME and location of where this data is stored.-- AlexHamilton - 20 Apr 2010

S11 fonction of the gate voltage

We can clearly observe a resonance which is really sharp and deep, but for a value of gate voltage of 0,54 which is much more than what Ben and Lasse observed. The matching resistance probably changed and is now much more important.

Transfer Function

The transfer function is really similar to what Ben got , but I cannot plot for higher resistance because the measurements where not sensible (cf text file attached).

• Can you plot against R2T? -- AlexHamilton - 20 Apr 2010
• I wasn't able to plot it against R2T or R4T because I wasn't able to read the current which was flowing through the Hall Bar, which was too low.

The problem is that the matching resistance is too high to be able to measure at the same time the resistance and the depth of the resonance (the Lock-in Amplifiers sensitivity isn't sufficient).

-> Why did the matching resistance change? (We checked the Ohmic and contact resistances with Olech and it's ok)

-> Change the AC Lock-in amplifier (to a more sensitive one?)

What Zac proposed :

- Let the dipstick in the dewar

-Use a more sensitive current amplifier on Monday

Resonance at 4K - 14/04/2010

Transfer Function

In this graphic we can notice that now the matching occurs at 35 kOhm, which is really close to what Lasse got (55kOhms).

Tests with the Demodulation Circuit :

Parameters

In order to test the demodulation circuit, we need first to make a list of all the parameters that can impact Vr, the voltage output ( Vr=sqrt(Vx^2+Vy^2) ):

- Frequency of the power supply : Linear dependance : Vr = -376.5+1.13*f(MHz)

- Amplitude of the power supply

- Phase shifter

- Amplifier

- AC Lock-in amplifier settings : excitation amplitude

- Resistance of the device (-> that's what we want to calibrate) : 600 MicroVolts of sensitivity for a resistance range of 10 000 Ohms -> Obviously not enough!

To see if we can follow the shift in the Resistance of the device with the demodulation circuit, we put a square wave oscillation excitation on the gate. We choosed the offset and the amplitude of the square wave oscillation so that we were on the slope of the transfer function.

Configuration 1 :

Frequency of the gate oscillation (square wave) : 5 kHz

Offset 0.2V

Amplitude 0.1V

The signal in yellow corresponds to the inphase and the one in green to the outphase.

We can observe a slight asymetry in the signal trace during the falling time. Relaxation Process, RC Time constant, 2nd Order Answer?

With Igor, I represent Vx (Inphase Signal from the Demodulation Circuit):

Level of Noise : 60-80 MicroVolts

Relaxation time when voltage down 50 MicroSeconds

Configuration 2 :

Frequency : 5 kHz

Offset 0.2V

Amplitude 0.1V

Tags

create new tag

Comments

How does this resonance compare to last time? It would be good to put a few lines at the top to explain what is different between this and the previous attempt.

-- AlexHamilton - 07 Apr 2010