Semiconductor device and method for measuring current of semiconductor device

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 VFN 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 transistor by substituting the determined α, β, and τ into Formula (a2):
• I
• O
• ⁢
• F
• ⁢
• F
• (
• t
• )
• =
• C
• S
• ×
• α
• ×
• β
• τ
• β
• ×
• t
• β
• -
• 1
• ×
• e
• -
• (
• t
• τ
• )
• β
• (
• a
• ⁢
• 2
• )
• wherein IOFF represents the off-state current of the first transistor and CS represents capacitance of the capacitor.