Zener Diode Breakdown

diodeex05.in : Zener Diode Breakdown

Requires: SSuprem 4/S-Pisces
Minimum Versions: Athena 5.22.3.R, Atlas 5.28.1.R

This example demonstrates electrical simulation of a Zener diode breakdown. It shows:

  • The formation of a 2D Zener diode structure in Athena
  • The transfer of the structure to Atlas
  • Specification of models for Zener breakdown simulation
  • Reverse bias simulation to the breakdown voltage

The structure formation is performed by implanting a heavy boron dose into a heavily doped n-type substrate. The 2D extent of the p+ region is controlled by the etch coordinate of an oxide mask. A short diffusion is performed in Athena to drive in the p+ dopant.

After the diffusion, extract statements are used to measure the junction depth and sheet resistance of the p+ region. After this, metal is added and patterned. The electrode positions are then defined using the electrode statements in Athena.

The statement go atlas enables the automatic interface from Athena to Atlas. DeckBuild will switch simulators to Atlas and load in the final Athena structure as the initial Atlas mesh.

In Atlas, the first lines of syntax define the models to be used in the simulation. The statement models bip defines the standard bipolar model set that is also recommended for diode simulation. This consists of concentration, temperature and electric field dependent mobilities, concentration dependent SRH and Auger recombination, and band gap narrowing. The parameter bbt.std enables the Lombardi band-to-band tunneling model. In heavily doped diodes this mechanism is the principal leakage current mechanism at voltages less than the avalanche breakdown. The impact statement enables the impact ionization model of Selberherr.

Newton's method is chosen on the method statement. The parameter climit=1e-4 is highly recommended for all reverse bias simulations in Atlas. It enables higher accuracy in the calculation of carrier concentration in the depletion regions.

The anode voltage is then ramped up to -10V in 0.25V steps. The breakdown voltage of this device is around -5.5V. Atlas will converge up to this voltage and then stop as no solutions beyond this voltage are possible. By plotting the output log file in TonyPlot, the breakdown can clearly be seen. The pre-breakdown current is dominated by band-to-band tunneling. An equivalent simulation excluding the 'bbt.std' parameter might be run to demonstrate this.

The final statements use the extract feature of DeckBuild to measure the maximum anode voltage at which convergence was obtained and the anode voltage for a particular value of anode current.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.