Lab 15b
Collect Digital Data

In this exercise you will use the LabVIEW™ software you created in exercise 14 to record the current generated by a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) current source.

Reading Assignment

Building Scientific Apparatus. Section 6.3.2 (Field-effect Transistors and MOSFETs).

Supplies and Materials

Serial Interface. FEEM Demo Apparatus (Optional). Digital multimeter (4-1/2 digit). BNC cable. BNC Adapter. Digital nanoammeter from Lab 10. USB-to-Serial adapter if your computer is USB Savvy. For example: http://www.keyspan.com/.

Note to Instructor: A FEEM Demo Apparatus can be used to demonstrate the quantum mechanical tunneling of electrons in vacuum.

I.    Introduction

The metal-oxide-semiconductor Field-effect transistor (MOSFET) is a building block of modern semiconductor devices. The first practical MOSFET was made in 1962 by Steven Hofstein and Fredric Heiman at the RCA research laboratory in Princeton, New Jersey. A MOSFET is a three terminal device. The insulated GATE controls the flow of current between the DRAIN and the SOURCE. See Figure 1.


Figure 1. An N-Type MOSFET

In the absence of a gate voltage the source and drain regions of the MOSFET are electrically isolated from each other and no current will flow between them. Notice that the metal gate film and the channel region of the semiconductor are separated by a thin, insulating layer of silicon dioxide. The silicon dioxide layer provides the MOSFET with a very high input impedance. MOSFETs are fabricated on either a P-type or an N-type substrate.

II.    Examine a Serial Interface

A serial interface provides a way to connect your digital nanoammeter to the serial port of a computer. The Contemporary Electronics interface contains a MOSFET current source. The current source is controlled by a front panel knob and integral ON/OFF switch An LED above the knob, when illuminated, indicates that the current source is active. Three Bayonet Navel Connectors (BNCs) and a socket for a digital nanoammeter provide external connections to the interface. The rear panel contains a power switch (illuminated when turned on), a connector for an external power supply (± 15 VDC) and a DB9  (RS-232) connector. See Figure 2.


Figure 2. A Serial Interface

Connect the wall transformer supplied with the serial interface to the rear panel connector labeled +15 VDC. Turn off the interface with the rear panel switch labeled Power. Insert your digital nanoammeter into the socket on the front panel (component side up). Connect the serial port of your computer to the rear panel connector labeled RS-232.

Always insert or remove your nanoammeter with the Interface turned off.

Turn on the interface with the rear panel switch labeled Power.

Turn off the current source by rotating the front panel knob fully counterclockwise. The integral switch should click OFF and red LED above the knob should not be illuminated.

III.    Detect a Serial interface

Open the CEsoftware folder. Double click CEsoftware.llb. Select Find Serial Interface from the Options menu. Record the number of the active serial port.

Proceed only if a Serial Interface and an active serial port are detected.

IV.    Prepare for Data Collection

The data collection apparatus consists of your nanoammeter inserted into a serial interface and a digital multimeter (DMM). Set the multimeter to the 20 VDC scale. Assemble the data collection apparatus. See Figure 3.


Figure 3. Data Collection Apparatus

V.    Collect Digital Data

Run the VI you saved in Lab 15 to collect digital data. Enter the number of the active serial port you recorded and select Vscale = 1.

Rotate the knob on the front panel of the serial interface clockwise to increase the current into your nanoammeter. The red LED above the knob should be illuminated. Click Enter on the front panel of your VI when the Op-amp indicator on the front panel reads:

  1. 0.025 V

  2. 0.050 V

  3. 0.100 V

  4. 0.250 V

  5. 0.500 V

  6. 1.000 V

  7. 2.000 V

  8. 3.000 V

  9. 4.000 V

  10. 5.000V

It is not necessary to match each voltage precisely. Speed is more important than precision because the op-amp output may fluctuate. Stop your measurement and call your instructor for assistance if the op-amp voltage on your VI is significantly different than the multimeter reading.

Click Quit on the front panel of your VI. Enter a file name and a location for data storage at the prompt. Turn off the current source by rotating the front panel knob fully counterclockwise. The integral switch should click OFF and red LED above the knob should not be illuminated.

VI.    Analyze Digital Data

Open the Fowler Nordheim analysis VI you created in Exercise 19 of GTutorial. Run the VI to analyze your digital data. If you have trouble with your VI double click CEsoftware.llb and select Analyze I-V Data from the Options menu.

Note to Instructor: For grading purposes ensure the student’s analysis VI is used.
VII.    References

M Lenzlinger and E. H. Snow. J. Appl. Phys. 40, 278-283 (1968).
Fowler-Nordheim Tunneling into Thermally Grown SiO2.pdf

Z. A. Weinberg. J. Appl. Phys. 53, 5052-5056 (1982).
On Tunneling in Metal-Oxide-Silicon Structures.pdf

VIII.    Homework Assignment

Update your lab notebook to include this exercise and questions raised in class.

Congratulations! You have completed Contemporary Electronics.