Semiconductor device and method for measuring current of semiconductor device

Patent metadata

Field	Value
Publication number	US-11600705-B2
Application number	US-202016775394-A
Country	US
Kind code	B2
Filing date	Jan 29, 2020
Priority date	Aug 25, 2014
Publication date	Mar 7, 2023
Grant date	Mar 7, 2023

Abstract

A semiconductor device in which a transistor has the characteristic of low off-state current is provided. The transistor comprises an oxide semiconductor layer having a channel region whose channel width is smaller than 70 nm. A temporal change in off-state current of the transistor over time can be represented by Formula (a2). In Formula (a2), IOFF represents the off-state current, t represents time during which the transistor is off, α and τ are constants, β is a constant that satisfies 0<β≤1, and CS is a constant that represents load capacitance of a source or a drain.IOFF⁡(t)=CS×α×βτβ×tβ-1×e-(tτ)β(a2)

First claim

What is claimed is:

1. A method for measuring an off-state current of a first transistor provided in a circuit, wherein the circuit comprises the first transistor, a second transistor, and a capacitor, and wherein a first terminal of the capacitor is electrically connected to one of a source and a drain of the first transistor and a gate of the second transistor, the method comprising the steps of:
writing charges to a first terminal of a capacitor through the first transistor;
making the first terminal of the capacitor in a floating state by turning off the first transistor;
measuring a current flowing between a source and a drain of the second transistor while the first transistor is kept off;
obtaining data on a correspondence between a potential of the first terminal of the capacitor and time elapsed after the first transistor is turned off;
performing fitting of Formula (a1) to the data to determine α, β, and τ,

V
FN

⁡

(
t
)

=

α
×

e

-

(

t
τ

)

β

(
a1
)

wherein V FN represents the potential of the first terminal of the capacitor, t represents the time elapsed after the first transistor is turned off, α and τ are constants, and β is a constant that satisfies 0<β≤1; and
calculating the off-state current of the first transistor by substituting the determined α, β, and τ into Formula (a2):

I
OFF

⁡

(
t
)

=

C
S

×

α
×
β

τ
β

×

t

β
-
1

×

e

-

(

t
τ

)

β

(
a2
)

wherein I OFF represents the off-state current of the first transistor and C S represents capacitance of the capacitor.

2. The method according to claim 1 , wherein a ground potential is supplied to a second terminal of the capacitor.

3. The method according to claim 1 , wherein the time elapsed after the first transistor is turned off is greater than or equal to 5×10 2 seconds and less than or equal to 1×10 5 seconds.

4. The method according to claim 1 , wherein the first transistor comprises an oxide semiconductor in a channel.

5. The method according to claim 1 , wherein the circuit is an characteristic evaluation circuit.

6. A method for measuring an off-state current of a first transistor provided in a circuit, wherein the circuit comprises the first transistor, a second transistor, and a capacitor, wherein one of a source and a drain of the first transistor, a gate of the second transistor, and a first terminal of the capacitor are electrically connected to a first node, the method comprising the steps of:
determining a correspondence between potentials written to the first node and values of currents flowing between a source and a drain of the second transistor;
writing charge to the first node by turning on the first transistor;
making the first node in a floating state by turning off the first transistor;
measuring a current flowing between the source and the drain of the second transistor while the first transistor is kept off;
generating data on a correspondence between a potential of the first node and time elapsed after the first transistor is turned off;
performing fitting of Formula (a1) to the data to determine α, β, and τ,

V

F
⁢
N

(
t
)

=

α
×

e

-

(

t
τ

)

β

(

a
⁢
1

)

wherein V FN represents the potential of the first node, t represents the time elapsed after the first transistor is turned off, α and τ are constants, and β is a constant that satisfies 0<β≤1; and
calculating the off-state current of the first

Assignees

• Semiconductor Energy Lab

Inventors

• Tsubuku Masashi
• Yamazaki Shunpei
• Kobayashi Hidetomo
• Ohshima Kazuaki
• Fujita Masashi
• Takeuchi Toshihiko

Classifications

• H10P74/207

  Electrical properties, e.g. testing or measuring of resistance, deep levels or capacitance-voltage characteristics · CPC title

• H10D84/811

  Combinations of field-effect devices and one or more diodes, capacitors or resistors · CPC title

• H10D86/481

  integrated with passive devices, e.g. auxiliary capacitors · CPC title

• H10D86/423

  comprising semiconductor materials not belonging to the Group IV, e.g. InGaZnO · CPC title

• H10D86/60

  wherein the TFTs are in active matrices · CPC title