3D Flash EPROM Programming

eprmex02.in : 3D Flash EPROM Programming

Requires: DevEdit 3D/Device 3D
Minimum Versions: Atlas 5.22.1.R

This examples demonstrates steady-state and transient simulation of an Flash EPROM device in three dimensions.

In this example an EPROM device is constructed using DevEdit 3D. The structure is then passed to Atlas for electrical testing. The input file consists of the following sections:

  • Construction of the device in DevEdit 3D
  • Threshold voltage test before programming
  • Transient simulation of Flash EPROM programming
  • Threshold voltage test after programming

The first stage of the input constructs the EPROM geometry, material regions, doping profiles, and electrodes in DevEdit 3D. The structure was created in DevEdit 3D by drawing the device regions in interactive mode and specifying 3D doping distribution. Finally the mesh was generated automatically by specifying basic mesh constraints and refining in the important areas of the device.

The Atlas simulation begins from reading in the structure from DevEdit 3D. DeckBuild provides an automatic interface between DevEdit and Atlas so that the structure produced by DevEdit 3D is transferred to Atlas without having to use the mesh statement.

In Atlas, the contact statements are used to assign the work function on the polysilicon gates and to specify the floating gate contact. The interface statement is used to assign a fixed interface charge under the floating gate. The models statement is used to select a set of physical models for programming simulation. The key model for programming is the hot carrier injection model to give the gate current. This is enabled by models hei .

First the initial solution for zero biases is obtained. Next, Id/Vgs calculations are performed with zero charge on the floating gate (before programming). The drain voltage is set to 0.5V, and the control gate voltage is ramped until the drain current reaches a compliance limit set with the 'compl' parameter. At this stage the combined algorithm is specified using method gummel newton . It means that if convergence is not reached in decoupled mode (gummel) the simulator will automatically switch to coupled mode (newton).

Next, the programming process is simulated. First of all, the control gate voltage is ramped to 10V. The combined algorithm is used for this stage, but the coupled Newton method is used for transient analysis calculations. In the transient analysis the drain voltage is ramped to 5.5V in 1ns. Vds is kept constant while transient programming is performed until the time set by tfinal is reached.

The final stage of the file re-simulates the Id/Vgs curve to obtain the threshold voltage after programming. The results of the two Id/Vgs curves can be overlaid using TonyPlot. extract statements can be used to measure the threshold according to user-defined rules. Details of the extract syntax for threshold voltage can be found under the MOS threshold voltage example. extract can also be used to measure the threshold voltage shift by subtracting the two previously extracted thresholds.

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