The MIT Microelectronics WebLab is a remote microelectronics device characterization laboratory. It allows users to measure the current-voltage characteristics of diodes and other microelectronics devices remotely, using a Java-enabled web browser. To run the Microelectronics WebLab, you must have a Java 1.4.2 plug-in installed, available from Sun's web site. You must also enable pop-ups.
Basic Diode Experiment
First, you will need to create an account at the WebLab web site. Account group permissions are manually approved; as a result, there may be up to a 24 hour delay between when you create the account, and when you can run the WebLab experiments. Once your account has been enabled, log in, and select the group appropriate for your class. Select the graphical client, and from there, select Launch Client. You may be asked whether you authorize the downloading of the WebLab client software to your computer; approve this. After a short download and startup time, the client should appear in a new window:
Figure 1: The WebLab 6.1 Client
We will now walk you through the simplest WebLab experiment - testing the properties of a PN diode. When the client is launched, it automatically makes the diode experiment available to you. The diode symbol has a triangle pointing into a vertical line. The diode is connected to an instrument that is going to perform the actual measurements - an Agilent 4155B Semiconductor Parameter Analyzer. The boxes labeled SMU1 and SMU2 correspond to the signal measurement ports of this 4155B. Characterizing the electrical behavior of the PN diode requires that these two SMU's be programmed appropriately.
Click on the box labeled SMU1. This will open a dialog box that allows you to configure SMU1. Since this is the anode, label the voltage Va and the current Ia. Check the download checkbox for both (WebLab will only allow you to plot the voltages and currents that you download). Set SMU1 to voltage mode, with the function set as Variable 1. Configure the voltage to sweep the voltage from -1.5V through 1.5V in 10mV increments. Do not adjust the compliance setting - this sets the maximum current that the 4155B will allow on any terminals, so as not to damage the device (this setting will be correctly preconfigured, and will depend on the type of diode currently in the system):
Figure 2: SMU1 Configuration
You will now want to configure SMU2. Instead of sweeping the voltage, you will want SMU2 connected to ground. As a result, set it to common mode. Since this is the cathode, label the voltage Vc and the current Ic. You do not need to download the voltage, since it is fixed. Also, the diode is a two-terminal device, so Ia=Ic. Therefore, there is no reason to download both Ia and Ic (downloading more variables will increase execution time of the experiment):
Figure 3: SMU2 Configuration
From the Measurement menu, select Run Measurement. Depending on the number of users, you may need to wait a short amount of time for the experiment to run. Once the experiment is run, you should see a plot of the IV characteristic of the diode:
Figure 4: Diode Characterization Results
In order to prevent damage to the diode, we have limited the maximum current (see the section on the compliance setting above). As a result, depending on the diode currently in the test setup, you may see the results saturate.
You can modify the axes from the dropdowns to the sides of the plot. Try switching the Y axis into logarithmic mode for a better idea of how the diode behaves.
After an experiment is run it is possible to download the experimental data to your machine. From the Results menu, you have the option of viewing the data in a pop-up window, or downloading it into a comma separated values (CSV) file suitable for Matlab, spreadsheets, or other applications.
Congratulations! You have successfully completed your first WebLab measurement.
Transistor Experiment
This tutorial walks you through a slightly more complicated experiment - analyzing a transistor.
First, if you have not already done so, you will need to create an account at the WebLab web site. Account group permissions are manually approved, and as a result, there may be up to a 24 hour delay between when you create the account, and when you can run the WebLab experiments. Once your account has been enabled, log in, and select the group appropriate for your class. Select the graphical client, and from there, select Launch Client. You may be asked whether you authorize the downloading of the WebLab client software to your computer; approve this. After a short download and startup time, the client should appear in a new window:
Figure 1: The WebLab 6.1 Client
Once loaded the client will be set to the default device, the diode. From the Devices menu, select 2n7000 MOSFET transistor:
Figure 2: WebLab with Transistor Selected
Now, we will configure the ports connected to the transistor. Click on SMU1, connected to the drain of the transistor. Name the voltage Vd, and the current Id. Download both, so that you can later plot them. Now, configure this port in voltage mode and as variable one, sweeping the voltage from 0V through 4V in 200mV increments:
Figure 3: SMU1 Configuration
Configure the gate terminal, SMU2, to use names Vg and Ig, voltage mode, function VAR2, a data range of 0.0V to 3.0V, and step size of 200mV. The compliance (maximum gate current) should be limited to 1.0 mA. Download the gate voltage. Unless you are particularly interested in gate leakage, there is no reason to download gate current:
Figure 4: SMU2 Configuration
The source terminal should be held at ground. You do this by configuring SMU3 using names Vs and Is, and setting the mode to COMM:
Figure 5: SMU3 Configuration
The experiment is ready to be submitted to the lab server. First, in case something goes wrong, you should save the current setup. From the setup menu, select Save setup. Setups are permanently saved to your account and may be loaded, edited, deleted or submitted whenever you login to the lab sever using this account.
Submit your experiment by selecting Run Measurement from the Measurement menu. Once the experiment is submitted to the lab server, the system will verify whether the experiment is properly configured. If not, it will display an error message telling you what the problem is. If the experiment passes the validation checks, it is placed on a queue. The "please wait" message is displayed. Depending on the number of experiments in the queue, the wait time for your experiment may vary. Once the experiment is complete, the results are downloaded to the client, and assuming the axes are reasonably configured, shown in the client window:
Figure 6: Output Result Plots
If your window does not show a similar plot, set the X1 axis to display Vd, the Y1 axis to display Id, Y2 axis to none, and all axes to Linear/autoscale. From here, try changing the variables and scales, and see how the plots change.
The Weblab client also allows you do define custom functions. In the next part of this tutorial, we will show how this can be used to plot small-signal conductance of the transistor. Select Show User-Defined Functions from the User Defined Functions menu. The User-Defined Functions window should open. Click the Add new function button in this window. Entering the the following information to create a named variable GD which is the derivative of drain current divided by drain voltage:
Figure 7: User Defined Functions Dialog
Resubmit your experiment to the server. Plot Id on the Y1 axis, and GD on the Y2 axis.
Figure 8: Plot with Custom Function
After an experiment is run it is possible to download the experiment data to your machine. From the Results menu item you have the option of viewing the data in a pop-up window, or downloading it into a comma separated values (CSV) file suitable for import into Matlab, a spreadsheet, or many other applications.