In this experiment, the relationship between breakdown voltage (VBD) and temperature was investigated for a signal diode and an unknown diode. The temperature was varied using a Vötsch VT4002 climate chamber while a variable current was supplied from the Keithley 2600 Series Sourcemeter . These parameters were controlled using an existing python script which was further developed to include climate chamber control. Some helpful information on how to get started with python can be found here. The python script used to perform this measurement will be provided near the bottom of this page.

Breakdown voltage

Breakdown in a diode occurs when a sufficiently large voltage is applied in reverse-bias, such that the device begins to conduct in reverse. Breakdown voltage is the minimum applied voltage that this occurs at. Diode breakdown is characterised by an exponential increase in current due to the avalanche effect, where accelerated charge carriers have sufficient energy to form further charge carriers from impacts with bound electrons. In the literature, a decrease in the breakdown voltage refers to its value moving towards 0 V, as this means breakdown can be achieved at lower reverse voltages.

Breakdown is understood to have a positive temperature coefficient, such that the breakdown voltage increases with increasing temperature. (Sze, 2006) This is due to avalanche breakdown being a band-to-band excitation process and the bandgap energy of silicon reducing with increasing temperature.

The figure above depicts the expected breakdown voltage dependency on temperature for varying doping concentration and both abrupt and linearly graded junctions, as per (Sze, 2006)

Experiment

The signal diode was measured in 10 °C steps between the temperatures of 10 to 50 °C. The Zener diode was measured in 5 °C steps between the temperatures of 10 to 35 °C.

As chamber temperatures tend to fluctuate upon reaching specified temperatures, the chamber remains at the specified temperature for 60 s before measuring. After this, the voltage sweep is applied. The signal diode has a VBD = -85.8 V at 10 °C . It increases slightly at 20°C and then sharply decreases to a value of -83.0V at 50 °C

The Zener diode shows a near constant VBD = -3.85 V , between 10 and 25 °C, with flucuations indistinguishable from noise. At 30 °C, a pronounced decrease to -3.8 V can be seen. It is possible that due to different Zener properties in reverse bias, the cutoff current was set at a too low value to see conclusive results.

Discussion

The resulting breakdown voltage - temperature relationship matches theoretical predictions; in that it follows a positive temperature coefficient. A signal diode is made for use in forward bias, so information on its breakdown voltage is sparse, however datasheets from the 1N4148/1N4448 signal diode show the Working Peak Reverse Voltage to be 75 V at 25 °C, which is in an appreciable range of what has been measured in this experiment. Further measurement of the Zener diode is needed to verify the abrupt change in breakdown voltage between 25 and 30 °C. It is likely however that the breakdown voltage was simply not reached with this diode as Zener diode typically can withstand much higher reverse voltages before breakdown occurs.

Python script used for perform the measurements

from KeithleyV15 import SMU26xx
from setupElab import eLabFTW
import matplotlib.pyplot as plt
import time
import datetime
import csv
import numpy as np
from voetsch import VT4002

"""
EXAMPLE: characteristic curve of a diode

Schematic:

--------------
    |            |
  -----         -|-
  | A | SMU     \|/
  -----         -|-
    |            |
    --------------

"""

# Connect to eLab and create an experiment
exp_title = "Breakdown at different T"
exp_description = "yellow diode reverse breakdown"
exp_date = datetime.datetime.now().strftime("%Y_%m_%d")
#
elab = eLabFTW()
elab.set_experiment(exp_title, exp_date,  exp_description)

""" ******* Connect to the Sourcemeter ******** """

# initialize the Sourcemeter and connect to it
# you may need to change the IP address depending on which sourcemeter you are using
sm = SMU26xx("TCPIP0::129.27.158.13::inst0::INSTR")

# get one channel of the Sourcemeter (we only need one for this measurement)
smu = sm.get_channel(sm.CHANNEL_A)

""" ******* Configure the SMU Channel A ******** """

# reset to default settings
smu.reset()
# setup the operation mode
smu.set_mode_voltage_source()
# set the voltage and current parameters
smu.set_voltage_range(100)
smu.set_voltage_limit(100)
smu.set_voltage(0)
smu.set_current_range(1E-6)
smu.set_current_limit(1E-6)
smu.set_current(0)

""" ******* Connect to the fridge ******** """
# define connection parameters for
ip_address = "129.27.158.42"
username = "simpacuser"   # fill in the username on the front of the climate chamber
password = "u1s2e3r4"   # fill in the password on the front of the climate chamber

# connect to the climate chamber
climate_chamber = VT4002(ip_address, username, password)

climate_chamber.enable()

# enable the output
smu.enable_output()

# define sweep parameters
sweep_start = -50
sweep_end = -100
sweep_step = 0.1
steps = abs(int((sweep_end - sweep_start) / sweep_step))

for Temp in range(1,6):
    T = 10*Temp
    climate_chamber.go_to_temperature(T, 0.2, 60)

#Read out the current temperature and print the result to the console
    currtemp = climate_chamber.get_actual_temperature()
    print('Current temperature (°C): ' + str(currtemp))

""" ******* For saving the data ******** """

# Create unique filenames for saving the data
    time_for_name = datetime.datetime.now().strftime("%Y_%m_%d_%H%M%S")
    filename_csv = 'SD_BD' + str(currtemp) + time_for_name +'.csv'
    filename_pdf = 'SD_BD' + str(currtemp) + time_for_name +'.pdf'

# Header for csv
    with open(filename_csv, 'a') as csvfile:
            writer = csv.writer(csvfile, delimiter=';',  lineterminator='\n')
            writer.writerow(["Voltage / V", "Current / A"])

""" ******* Make a voltage-sweep and do some measurements ******** """

# define variables we store the measurement in
    data_current = []
    data_voltage = []

# step through the voltages and get the values from the device
    for nr in range(steps):
        # calculate the new voltage we want to set
        voltage_to_set = sweep_start -(sweep_step * nr)
        # set the new voltage to the SMU
        smu.set_voltage(voltage_to_set)
        # get current and voltage from the SMU and append it to the list so we can plot it later
        [current, voltage] = smu.measure_current_and_voltage()
        data_voltage.append(voltage)
        data_current.append(current)
        print(str(voltage)+' V; '+str(current)+' A')
        # Write the data in a csv
        with open(filename_csv, 'a') as csvfile:
            writer = csv.writer(csvfile, delimiter=';',  lineterminator='\n')
            writer.writerow([voltage, current])
    smu.set_voltage(0)

""" ******* Plot the Data we obtained ******** """
    
    plt.plot(data_voltage, data_current,'x-', linewidth=2)

# set labels and a title
    plt.xlabel('Voltage / V', fontsize=14)
    plt.ylabel('Current / A', fontsize=14)
    plt.title('Characteristic curve of a signal diode', fontsize=14)
    plt.tick_params(labelsize = 14)
    plt.tight_layout()
    plt.savefig(filename_pdf)
    
    plt.clf()
    
    # Upload files to eLab
    elab.upload_file(filename_csv)
    elab.upload_file(filename_pdf)
    elab.upload_script(__file__)

#Bring the climate chamber to room temperture so you can safely open it
#climate_chamber.go_to_temperature(23, 2, 60)

# disable the output
smu.disable_output()

# properly disconnect from the device
sm.disconnect()

climate_chamber.disable()

breakdown_temp_sweep.py

Breakdown voltage of diodes at different temperatures

Breakdown voltage

Experiment

Discussion

Python script used for perform the measurements