Threshold voltage measurement device

• US 8,582,378 B1
• Filed: 08/29/2012
• Issued: 11/12/2013
• Est. Priority Date: 05/11/2012
• Status: Active Grant

• Current Assignee: National Chiao Tung University (Government of The Republic of China)
• Original Assignee: National Chiao Tung University (Government of The Republic of China)
• Inventors: Jou, Shyh-Jye, Lin, Yi-Wei, Shih, Wei-Chiang, Lien, Nan-Chun, Lee, Kuen-Di, Chuang, Ching-Te, Lin, Geng-Cing, Wang, Shao-Cheng, Tsai, Ming-Chien, Chu, Jyun-Kai
• Primary Examiner(s): Byrne, Harry W
• Assistant Examiner(s): REIDLINGER, RONALD LANCE
• Application Number:
  US13/597,733
• Publication Number:
  US 20130301343A1
• Time in Patent Office: 440 Days
• Field of Search: 365/154, 365/156, 365/201, 714/721, 324/762.01, 324/762.09
• US Class Current: 365/201
• CPC Class Codes: G11C 11/41 forming static cells with positive feedback, i.e. cells not needing refreshing or charge regeneration, e.g. bistable multivibrator or Schmitt trigger
• CPC Class Codes: G11C 29/12005 comprising voltage or current generators
• CPC Class Codes: G11C 29/50004 of threshold voltage

Abstract

A threshold voltage measurement device is disclosed. The device is coupled to a 6T SRAM. The SRAM comprises two inverters each coupled to a FET. Power terminals of one inverter are in a floating state; the drain and source of the FET coupled to the inverter are short-circuited. Two voltage selectors, a resistor, an amplifier and the SRAM are connected in a negative feedback way. Different bias voltages are applied to the SRAM for measuring threshold voltages of two FETs of the other inverter and the FET coupled to the other inverter. The present invention uses a single circuit to measure the threshold voltages of the three FETs without changing the physical structure of the SRAM. Thereby is accelerated the measurement and decreased the cost of the fabrication process and measurement instruments.

Claims

1. A threshold voltage measurement device, which is connected with a 6T-SRAM (Static Random Access Memory) that comprises a first FET (Field Effect Transistor), a second FET, a third FET, an inverter, and a fourth FET, wherein said first FET connects with a first bit line and a word line, and wherein said second FET and said third FET respectively have a first power terminal and a second power terminal, and wherein a third power terminal and a fourth power terminal of said inverter are in a floating state, and wherein said fourth FET connects with a second bit line and said word line, and wherein a drain and a source of said fourth FET are short-circuited, and

wherein said threshold voltage measurement device comprises

an amplifier outputting an amplified voltage, wherein a negative input of said amplifier connects with said first bit line and connects with a power supply terminal via a resistor, and wherein a positive input of said amplifier connects with a preset positive voltage;

a first voltage selector receiving a digital voltage, connecting with said amplifier and said second bit line, and selecting to apply said digital voltage or said amplified voltage to said second bit line; and

a second voltage selector receiving a first high voltage, connecting with said amplifier and said word line, and selecting to apply said first high voltage or said amplified voltage to said word line, wherein said threshold voltage measurement device operates to meet requirements of different measurements respectively according to a first operation mode, a second operation mode and a third operation mode,

wherein in said first operation mode, a second high voltage is applied to said first power terminal and said second power terminal;

said first voltage selector selects to apply said digital voltage to said second bit line;

said second voltage selector selects to apply said amplified voltage to said word line;

a first low voltage is applied to said power supply terminal to let a current value of said resistor under a voltage drop between said first low voltage and said preset positive voltage equal a current value of said first FET when a first gate-source voltage (V_GS1) of said first FET equals a first threshold voltage of said first FET, whereby a first current flows out from said first power terminal or said second power terminal and passes through said first FET and said resistor in sequence to said power supply terminal;

while a voltage of said negative input equals said preset positive voltage, said first threshold voltage is obtained via said amplified voltage, and

wherein in said second operation mode, a third low voltage and said preset positive voltage are respectively applied to said first power terminal and said second power terminal;

said first voltage selector selects to apply said amplified voltage to said second bit line;

said second voltage selector selects to apply said first high voltage to the word line;

a fourth high voltage is applied to said power supply terminal to let a current value of said resistor under a voltage drop between said fourth high voltage and said preset positive voltage equal a current value of said second FET when a second gate-source voltage (V_GS2) of said second FET equals a second threshold voltage of said second FET, whereby a second current flows out from said power supply terminal and passes through said resistor, said first FET and said second FET in sequence to said first power terminal;

while a voltage of said negative input equals said preset positive voltage, said second threshold voltage is obtained via said amplified voltage, and

wherein in said third operation mode, said preset positive voltage and a third high voltage are respectively applied to said first power terminal and said second power terminal;

said first voltage selector selects to apply said amplified voltage to said second bit line;

said second voltage selector selects to apply said first high voltage to said word line;

a second low voltage is applied to said power supply terminal to let a current value of said resistor under a voltage drop between said second low voltage and said preset positive voltage equal a current value of said third FET when a third gate-source voltage (V_GS3) of said third FET equals a third threshold voltage of said third FET, whereby a third current flows out from said second power terminal and passes through said third FET, said first FET and said resistor in sequence to said power supply terminal;

while a voltage of said negative input equals said preset positive voltage, said third threshold voltage is obtained via said amplified voltage.

2. The threshold voltage measurement device according to claim 1, wherein in said first operation mode, said first threshold voltage equals an absolute value of a difference between said amplified value and said preset positive voltage.

3. The threshold voltage measurement device according to claim 1, wherein in said second operation mode, said second threshold voltage equals an absolute value of a difference between said amplified value and said preset positive voltage.

4. The threshold voltage measurement device according to claim 1, wherein in said third operation mode, said third threshold voltage equals an absolute value of a difference between said amplified value and said preset positive voltage.

5. The threshold voltage measurement device according to claim 1, wherein when said digital voltage is a high level voltage, said first current flows out from said second power terminal.

6. The threshold voltage measurement device according to claim 1, wherein when said digital voltage is a low level voltage, said first current flows out from said first power terminal.

7. The threshold voltage measurement device according to claim 1, wherein a gate of said first FET connects with said word line, and wherein a drain of said first FET connects with first bit line, and wherein a drain of said second FET functions as said first power terminal, and wherein a source of said second FET connects with a source of said first FET, and wherein a drain of said third FET functions as said second power terminal, and wherein a source of said third FET connects with said source of said first FET and said inverter, and wherein a gate of said third FET connects with a gate of said second FET, said inverter, and a source of said fourth FET, and wherein a gate and a drain of said fourth FET respectively connects with said word line and said second bit line.

8. The threshold voltage measurement device according to claim 1, wherein said inverter includes

a fifth FET, wherein a drain of said fifth FET functions as said third power terminal;

and

a sixth FET, wherein a drain of said sixth FET functions as said fourth power terminal, and wherein a source of said sixth FET connects with a source of said fourth FET and gates of said second FET and said third FET, and wherein a gate of said sixth FET connects with a gate of said fifth FET and sources of said first FET, said second FET and said third FET.

9. The threshold voltage measurement device according to claim 8, wherein said fifth FET and said sixth FET are respectively a P-channel FET and an N-channel FET.

10. The threshold voltage measurement device according to claim 1, wherein said first FET, said third FET and said fourth FET are N-channel FETs, and wherein said second FET is a P-channel FET.