RFID tag having non-volatile memory device having floating-gate FETs with different source-gate and drain-gate border lengths
Non-volatile memory (NVM) devices are disclosed. In one aspect, a NVM device may include a substrate, and a field-effect transistor (FET). The FET may include a first doped region in the substrate and a second doped region in the substrate. The first and the second doped regions may define a channel region of the substrate between them. An insulating layer may overlie the channel region. A floating gate may overlie the insulating layer. Charge of an amount that encodes a value may be stored on the floating gate. The floating gate and the first and the second doped regions may be shaped such that the floating gate defines with the first doped region a first border of a first length, and the floating gate defines with the second doped region a second border of a second length that is less than 90% of the first length.
1. A method, comprising:
biasing a field-effect transistor (FET) of a non-volatile memory (NVM) to inject electrons onto a floating gate of the FET;
differentially and capacitively drawing at least 10% more charge carriers from the floating gate toward a first doped region of the FET than toward a second doped region of the FET;
causing charge carriers to flow through a channel region of the FET between the first dope region and the second doped region to store a value; and
storing charge of an amount that encodes the value on the floating gate by injecting the electrons onto the floating gate of the FET while the charge carriers flow through the channel region of the biased FET.
2. The method of claim 1 , wherein the electrons are injected onto the floating gate without controlling a voltage of the floating gate.
3. The method of claim 2 , wherein differentially and capacitively drawing comprises drawing the charge carriers of the floating gate toward a first border between the floating gate and the first doped region that is at least 10% longer than a second border between the floating gate and the second doped region.
4. The method of claim 3 , wherein drawing the charge carriers toward the first border comprises drawing the charge carriers toward a first border that is substantially straight.
5. The method of claim 3 , wherein drawing the charge carriers toward the first border comprises drawing the charge carriers toward a first border that is substantially not straight.
6. The method of claim 3 , wherein drawing the charge carriers toward the first border comprises drawing the charge carriers toward a border of a portion selected from: (i) a portion of the first doped region that protrudes towards the second doped region; and (ii) a portion of the first doped region that recedes from the second doped region.
7. The method of claim 3 , wherein drawing the charge carriers toward the first border comprises drawing the charge carriers to a first border that is from 1.15 to 5 times longer than the second border.
8. The method of claim 1 , wherein injecting the electrons comprises injecting the electrons by one selected from impact ionized hot-electron injection (IHEI) and channel hot-electron injection (CHEI).
9. The method of claim 1 , wherein the FET is included in a radio-frequency identifier (RFID) tag.
10. The method of claim 3 , wherein the first border is not parallel with respect to the second border.
11. The method of claim 3 , wherein a length of the second border is 20% to 85% of a length of the first border.