Abstract
Today, no practical coupling ratios extracting technique is proposed in split-gate Flash memory. But there are many proposed coupling ratios extraction methods for stacked-gate Flash memory. The main differences between split-gate and stacked-gate Flash memory are the special control-gate structure (split structure) and read operation (no threshold voltage definition) of split-gate Flash memory. So many coupling ratios extracting technique in stacked-gate Flash memory are not suitable for split-gate Flash memory. This paper introduces a novel coupling ratios extracting technique to extract the most important coupling ratios, control-gate coupling ratio and source coupling ratio, of split-gate Flash memory. From the source side Constant Ramp Rate Programming (CRRP) method, we can extract the source coupling ratio. According to the simulation results of MEDICI 2D potential contour distribution, when the device is under programming operation, after the floating-gate potential reaching the convergent point, the bulk voltage has no influence on the surface potential distribution in the region under the floating-gate. And the depletion region of high voltage source replaces the contact area of bulk to floating-gate. The coupling ratio of bulk is small enough to be negelected. According to the capacitance model of split-gate device, and the assumption of bulk couplig ratio is small under programming operation, control-gate coupling ratio and source coupling ratio are knowen. Based on these coupling ratios, we can construct the electrical model of split-gate Flash memory. The electrical model is useful in improveing the device's characteristic and operation condition of split-gate Flash memory. And it will play a important role in the design of next generation device in the future. Accroding to the experimential results, a new coupling ratio extraction scheme is proposed for spilt-gate Flash memories with advantages of : 1. In sti extraction under programming operation 2. Feasible extracting measurement 3. De-couple the source coupling ratio from the others 4. Insensitive to measuring parameters 5. Reflection of devices' geometric dimensions