A method and apparatus for testing double-layer transistor mobility

Abstract

The application provides a method and device for testing double-electric-layer transistor mobility, comprising the following steps: applying a direct current signal to a gate and a drain of the double-electric-layer transistor respectively, and superimposing an alternating current signal on the gate of the double-electric-layer transistor; measuring the current flowing from the gate to the source and the current flowing from the drain to the source under the premise of superimposing the alternating current signal; realizing real-time monitoring of the capacitance and the transconductance based on the measured current; and calculating the mobility of the double-electric-layer transistor based on the real-time monitored capacitance and transconductance.

Description

Technical Field

[0001] This invention belongs to the field of transistor mobility testing technology, and particularly relates to a method and apparatus for testing the mobility of double-layer transistors. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] The gate dielectric layer of field-effect transistors (FETs) uses solid insulating layers such as silicon dioxide, aluminum oxide, and hafnium oxide, and its specific capacitance is approximately 10⁻⁶. -7 F / cm 2 The induced carrier density is approximately 10. 13 cm -2 Due to their low capacitance and low breakdown voltage, it is difficult to further increase the carrier density and reduce the operating voltage. Ionic liquids (ILs) have advantages such as a large electrochemical window, high thermal and chemical stability, and non-toxicity and non-volatile properties. Devices that use ILs to replace the solid insulating layer of traditional FETs are called electric double-layer transistors (EDLTs).

[0004] Double-layer transistors using ionic liquids as gate dielectrics form sub-nanometer-scale electric double layers (EDLs) at both the channel / electrolyte interface and the gate / electrolyte interface, resulting in large capacitance and low operating voltage, with a specific capacitance exceeding 10. -6 F / cm 2 The carrier density can reach 10 15 cm -2 The operating voltage is as low as 1V.

[0005] Due to their advantages such as large capacitance and low voltage, double-layer transistors have wide applications in logic circuits, nervous systems and synaptic devices, portable sensors, displays, and other fields. Unlike traditional solid insulating layers, ionic liquids contain a large number of mobile anions and cations. The movement of anions and cations in ionic liquids requires a certain amount of time, and the charging and discharging process takes several milliseconds. As a result, the capacitance of double-layer transistors is frequency-dependent.

[0006] Furthermore, the transfer curves of the double-layer transistor differ at different test speeds, indicating that transconductance is also frequency-dependent. Since both the capacitance and transconductance of a double-layer transistor change with frequency, and it's impossible to obtain the capacitance and transconductance at the same frequency under DC conditions, but calculating mobility requires capacitance and transconductance at the same frequency, the mobility of a double-layer transistor can no longer be calculated using the traditional methods for thin-film transistors (TFTs).

[0007] Currently, research on electric double-layer transistors typically uses capacitance at a relatively low frequency and transconductance under DC conditions to calculate mobility. The drawback of this method is that the transconductance is not the same as the capacitance at a specific frequency, and the mobility obtained will differ depending on the chosen frequency. Therefore, the mobility calculated using this method is merely an estimate. However, mobility is a crucial and indispensable parameter in device performance characterization and applications. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the present invention provides a method for testing the mobility of electric double-layer transistors, which realizes real-time monitoring of capacitance and transconductance, and obtains the capacitance and transconductance of the sample under test at the same frequency to accurately calculate the mobility of EDLTs.

[0009] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0010] In the first aspect, a method for testing the mobility of a double-layer transistor is disclosed, including:

[0011] A DC signal is applied to the gate and drain of the double-layer transistor, and an AC signal is superimposed on the gate of the double-layer transistor.

[0012] The current from the gate drain to the source and the drain, as well as the current from the drain to the source through the channel, are measured under the premise of superimposed AC signal.

[0013] The capacitance and transconductance at each frequency are monitored in real time based on the measured current, and the mobility of the double-layer transistor is calculated based on the monitored capacitance and transconductance.

[0014] As a further technical solution, a DC voltage is provided to the gate and drain through a DC source, an AC signal is superimposed on the gate through an AC signal generator, and the current is measured at the source and drain terminals through a current tester.

[0015] As a further technical solution, the current flowing through the two current testers can be expressed as follows:

[0016] I in-1 =A·i ⊥ +C·i || +I ||

[0017] I in-2 =-B·i ⊥ -D·i || +I || ;

[0018] Among them, i ⊥ It is the 90° phase current generated by a double-layer transistor under AC signal conditions;

[0019] i || It is the 0° phase current from the gate drain to the source and drain;

[0020] I || It is the 0° phase current from the drain to the source through the channel;

[0021] A, B, C, and D represent the coefficients of the current in each part, and A+B=1, C+D=1, A=C, B=D.

[0022] As a further technical solution, i is obtained based on the expression of the current flowing through the two current testers. ⊥ and I || Based on the obtained i ⊥ and I || The formulas for calculating capacitance and transconductance are as follows:

[0023] Capacitor is represented as:

[0024]

[0025] Transconductance is represented as:

[0026]

[0027] As a further technical solution, mobility includes linear mobility and saturation mobility;

[0028] The linear mobility is expressed as:

[0029]

[0030] The saturation mobility is expressed as:

[0031]

[0032] As a further technical solution, the change of threshold voltage over time can be obtained by real-time monitoring of the current change of the double-layer transistor of the device under test, which can be used to test the bias stability of the device.

[0033] Secondly, a device for testing the mobility of a double-layer transistor is disclosed, comprising:

[0034] DC power supply, AC signal generator and current tester;

[0035] The DC source provides DC voltage applied to the gate and drain of the electric double-layer transistor;

[0036] The AC signal generator is used to superimpose an AC signal onto the gate of the electric double-layer transistor;

[0037] The current tester is used to measure the current from the gate to the source and the drain, as well as the current from the drain to the source through the channel, under the premise of superimposed AC signal.

[0038] The capacitance and transconductance at each frequency are monitored in real time based on the measured current, and the mobility of the double-layer transistor is calculated based on the monitored capacitance and transconductance.

[0039] As a further technical solution, a processor is also included, which receives the current measured by the current tester and calculates the capacitance and transconductance based on the current value, and then calculates the linear mobility and saturation mobility based on the capacitance and transconductance.

[0040] As a further technical solution, the current tester is a lock-in amplifier, which separates the DC component and the AC component.

[0041] As a further technical solution, the double layer of the double-layer transistor can be an ionic liquid, and the active layer can be an oxide semiconductor.

[0042] The above one or more technical solutions have the following beneficial effects:

[0043] The technical solution of this invention obtains the current generated by the capacitor under AC signal, the current from the gate to the source and drain, and the current from the drain to the source through the channel, thereby realizing real-time monitoring of capacitance and transconductance. The capacitance and transconductance of the sample under test at the same frequency are obtained to accurately calculate the mobility of EDLTs.

[0044] The technical solution of this invention superimposes an AC signal onto a DC signal, measures and analyzes the current flowing through two current testers, and can directly calculate the capacitance and transconductance at that frequency, and then calculate the mobility of EDLTs. This method solves the problem that the capacitance and transconductance at the same frequency cannot be obtained under DC conditions.

[0045] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0046] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0047] Figure 1 This is a schematic diagram of the transfer curves of EDLTs at different test speeds in an embodiment of the present invention;

[0048] Figure 2 This is a diagram of the experimental testing apparatus according to an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram illustrating the change in linear region mobility with frequency according to an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram illustrating the change in mobility in the saturated region with frequency according to an embodiment of the present invention. Detailed Implementation

[0051] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0052] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0053] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0054] Unlike traditional solid insulating layers, ionic liquids (ILs) contain a large number of mobile anions and cations. When a positive voltage is applied to the gate, anions move towards the gate, while cations move in the opposite direction. When a negative voltage is applied, cations move towards the gate, while anions move in the opposite direction. Therefore, within a certain reaction time, ionic liquids (EDLs) will form at the interface between the gate and the ILs, as well as at the interface between the ILs and the channel. Because the movement speed of anions and cations in ILs is relatively slow, at low frequencies, ions have sufficient reaction time to form EDLs, while at high frequencies, ions do not have enough time to react and EDLs cannot be formed. Therefore, when ILs are used as the gate dielectric, the capacitance of EDLs varies with frequency because the movement of anions and cations requires a certain amount of time.

[0055] Figure 1 The transfer curves of EDLTs measured at different speeds are shown. The experimental results show that as the test speed decreases, the transfer curve shifts to the left. The slope of the transfer curve is the transconductance. Obviously, different test speeds will result in different transconductances, that is, the transconductance of EDLTs also changes with frequency.

[0056] TFTs use solid-state insulating layers, and their capacitance and transconductance do not change with frequency. Therefore, the mobility of TFTs can be directly calculated using the transconductance at DC and the capacitance at any frequency. However, for EDLTs using ILs as insulating layers, since their capacitance and transconductance both change with frequency, some research groups currently use DC transconductance and capacitance at lower frequencies to calculate the mobility of EDLTs based on TFT mobility calculation methods. Obviously, these capacitance and transconductance values ​​are not at the same frequency. To accurately calculate the mobility of EDLTs, it is necessary to obtain the capacitance and transconductance of the sample under test at the same frequency.

[0057] Example 1

[0058] This embodiment discloses a method for testing the mobility of electric double-layer transistors (EDLTs). Taking into account the characteristics of capacitance and transconductance of EDLTs changing with frequency, an AC signal is superimposed on a DC signal. The mobility of EDLTs is calculated by testing the capacitance and transconductance of each part of the current in real time at each frequency, so as to solve the current problem that it is impossible to accurately calculate the mobility of EDLTs.

[0059] To more clearly illustrate this embodiment, the implementation process of testing the mobility of the double-layer transistor can be specifically described as follows:

[0060] like Figure 2 As shown, this invention proposes a method for detecting the transconductance and mobility of EDLTs at different frequencies by coupling DC and AC signals. Specifically, the method involves providing voltages V0 to the gate and drain via a DC source. G and voltage V D An AC signal is superimposed on the gate using an AC signal generator. Since the gate already has a DC signal due to the applied voltage from the DC source, the AC signal is superimposed on this DC signal. The current at the source and drain is measured using a current meter. The current formulas for the linear and saturation regions of the EDLTs after superimposing the AC signal are expressed as formulas (1) and (2), respectively. DS-lin and I DS-sat For V respectively GS Differentiating, we obtain formulas (3) and (4). According to formula (3), the linear mobility can be expressed as formula (5). The g in formula (4) m-sat For V GS Taking the differential, the resulting slope is expressed as formula (6), and thus the saturated mobility can be expressed as formula (7). According to the above formulas, it can be seen that to calculate the mobility, the capacitance and transconductance need to be calculated, and the other parameters are known.

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068] Among them I DS-lin and I DS-sat These represent the linear and saturation currents, respectively. W is the channel width, L is the channel length, and μ is the channel width. ac-lin and μ ac-sat These are linear mobility and saturation mobility, C. ox-ac It's a capacitor, V GS It is the gate-source voltage, ν ac It is alternating voltage, V TH It is the threshold voltage, V DS It is the source-drain voltage, g m-lin and g m-sat These are the transconductances in the linear and saturation regions, respectively.

[0069] Among them, the formula for the linear region current after superimposing the AC signal is based on the TFT current formula under DC. The obtained superimposed AC signal is embodied in formula (1) (V GS +v ac V GS Indicates a DC signal, v ac It is a superimposed AC signal. The formula for the saturation region current is similar.

[0070] The process of calculating capacitance and transconductance is as follows:

[0071] The method proposed in this invention applies a DC voltage to the gate of the sample under test and superimposes a sinusoidal AC signal, while applying a DC voltage V to the drain. D The source is grounded. The current flowing through the two current meters can be expressed as: I in-1 =A·i ⊥ +C·i || +I || and I in-2 =-B·i ⊥ -D·i || +I || .

[0072] Where i ⊥ It is the 90° phase current generated by EDLs under AC signal;

[0073] i ||It is the 0° phase current from the gate drain to the source and drain;

[0074] I || It is the 0° phase current from the drain to the source through the channel;

[0075] A, B, C, and D represent the coefficients of the current in each part, and A+B=1, C+D=1, A=C, B=D.

[0076] Capacitance can be represented as Transconductance can be expressed as Therefore, we only need to find i ⊥ and I || The capacitance and transconductance can then be calculated, and thus the mobility can be calculated, where C ox-ac It is a capacitor, ν ac It is alternating voltage, g m It is transconductance, and f is frequency.

[0077] Figure 3 , Figure 4 The graph shows the mobility of EDLTs in the linear and saturation regions as a function of frequency, with the dashed line perpendicular to the X-axis representing the cutoff frequency. The square dotted line represents the mobility calculated using the DC method, showing that the mobility in both the linear and saturation regions changes with frequency. The triangular dotted line represents the mobility calculated using the AC method proposed in this invention. The results show that the mobility calculated using the capacitance and corresponding transconductance obtained by this method does not change with frequency within the cutoff frequency range, but the mobility increases rapidly with frequency at higher frequencies. This is because EDLTs only operate at low frequencies; at higher frequencies, ions do not have enough time to react and form EDLs. This part of the data is unreliable; only the data at low frequencies should be considered.

[0078] This invention provides a method for detecting the transconductance and mobility of EDLTs at different frequencies using DC and AC coupling, including a DC source providing voltage to the gate and drain, an AC signal generator superimposing an AC signal on the gate, and a current meter measuring the current across the source and drain.

[0079] The current tester section can be a lock-in amplifier with a parallel resistor (R), because it is a DC signal superimposed on an AC signal, and the lock-in amplifier can separate the DC component and the AC component.

[0080] Specifically, in this embodiment, the current is obtained by using the output voltage of a lock-in amplifier and the parallel resistor (R). The current can also be directly measured by other instruments. Here, the current testers 1 and 2 are replaced by lock-in amplifiers 1 and 2, respectively. Lock-in amplifier 1 can directly output the voltage across the parallel resistor (R), including the 0° phase (X1) and the 90° phase (Y1). Similarly, lock-in amplifier 2 can also directly output the voltage across the parallel resistor (R), including the 0° phase (X2) and the 90° phase (Y2). These can be expressed as formulas (8)-(11), respectively. Formula (8) plus (10) is easy to obtain. Formula (9) plus (11) yields Formula (9) yields From A=C, we get i.e. i ⊥ and I || Both can be calculated from the output of the lock-in amplifier and the resistor (R) with a known resistance value.

[0081] In summary, by calculating the output values ​​(X1, Y1, X2, Y2) of the experimental device proposed in this invention and the parallel resistors, the values ​​of capacitance and transconductance at the same frequency can be obtained. The accurate mobility of EDLTs can be calculated from this set of capacitance and transconductance at the same frequency.

[0082] X1=R·(C·i || +I || (8)

[0083] Y1=R·(A·i ⊥ (9)

[0084] X2=-R·(I || -D·i || )=R·(D·i || -I || (10)

[0085] Y2=-R·(-B·i ⊥ )=R·(B·i ⊥ (11)

[0086] The technical solution of this invention can also calculate the cutoff frequency of the sample being tested.

[0087] 90° phase current i generated through the double layer under AC signal ⊥ The 0° phase current I from the drain to the source through the channel || The ratio is the current gain, i.e., the current gain. Depend on have to Where ω = 2πf. The frequency f when α = 1 is the cutoff frequency of the EDLT.

[0088] The technical solution of this invention can monitor the change of current of the device under test over time in real time and obtain the change of threshold voltage over time. The current formula contains the threshold voltage, and the threshold voltage can be directly obtained by measuring the current. The change of threshold voltage over time is the so-called bias stability, which can be used to test the bias stability of the device.

[0089] The electric double layer of a double-layer transistor can be an ionic liquid, and the active layer can be an oxide semiconductor.

[0090] Example 2

[0091] The purpose of this embodiment is to provide a testing device for the mobility of double-layer transistors, comprising:

[0092] DC power supply, AC signal generator and current tester;

[0093] The DC source provides DC voltage applied to the gate and drain of the electric double-layer transistor;

[0094] The AC signal generator is used to superimpose an AC signal onto the gate of the electric double-layer transistor;

[0095] The current tester is used to measure the current from the gate to the source and the drain, as well as the current from the drain to the source through the channel, under the premise of superimposed AC signal.

[0096] Real-time monitoring of capacitance and transconductance is achieved based on measured current, and the mobility of the double-layer transistor is calculated based on the real-time monitored capacitance and transconductance.

[0097] In a specific implementation example, a processor is also included. The processor receives the current measured by the current tester and calculates the capacitance and transconductance based on the current value. Then, it calculates the linear mobility and saturation mobility based on the capacitance and transconductance.

[0098] For the specific testing method of this device, please refer to the detailed steps in Example 1.

[0099] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for testing the mobility of an electric double-layer transistor, characterized in that, include: A DC signal is applied to the gate and drain of the double-layer transistor, and an AC signal is superimposed on the gate of the double-layer transistor. The current from the gate drain to the source and the drain, as well as the current from the drain to the source through the channel, are measured under the premise of superimposed AC signal. Real-time monitoring of capacitance and transconductance at each frequency is achieved based on measured current, and the mobility of the double-layer transistor is calculated based on the real-time monitored capacitance and transconductance. The current is measured across the source and drain terminals using a current tester. The currents flowing through the two current testers are expressed as follows: and ; in, It is the 90° phase current generated by a double-layer transistor under AC signal conditions; It is the 0° phase current from the gate drain to the source and drain; It is the 0° phase current from the drain to the source through the channel; A, B, C, and D represent the coefficients of the current in each part, and A+B=1, C+D=1, A=C, B=D; The expression for the current flowing through the two current meters is obtained. and Based on the obtained and The formulas for calculating capacitance and transconductance are as follows: Capacitor is represented as: ； Transconductance is represented as: ； Among them, C ox-ac It is a capacitor, ν ac It is alternating voltage, g m It is transconductance, and f is frequency.

2. The method for testing the mobility of a double-layer transistor as described in claim 1, characterized in that, A DC voltage is provided at the gate and drain through a DC source, and an AC signal is superimposed on the gate through an AC signal generator.

3. The method for testing the mobility of a double-layer transistor as described in claim 1, characterized in that, Mobility includes linear mobility and saturation mobility; The linear mobility is expressed as: = ； The saturation mobility is expressed as: = ； Where W is the channel width, L is the channel length, and μ ac-lin and μ ac-sat These are linear mobility and saturation mobility, V DS It is the source-drain voltage, C ox-ac It's a capacitor, g m-lin It is the transconductance in the linear region, and the slope is the transconductance in the saturation region. m-sat For gate-source voltage V GS Find the slope obtained by differentiation.

4. The method for testing the mobility of a double-layer transistor as described in claim 1, characterized in that, By monitoring the change in current over time of the double-layer transistor of the device under test in real time, the change in threshold voltage over time can be obtained, which can be used to test the bias stability of the device.

5. A device for testing the mobility of an electric double-layer transistor, characterized in that, include: DC power supply, AC signal generator and current tester; The DC source provides DC voltage applied to the gate and drain of the electric double-layer transistor; The AC signal generator is used to superimpose an AC signal onto the gate of the electric double-layer transistor; The current tester is used to measure the current from the gate to the source and the drain, as well as the current from the drain to the source through the channel, under the premise of superimposed AC signal. Real-time monitoring of capacitance and transconductance at each frequency is achieved based on measured current, and the mobility of the double-layer transistor is calculated based on the real-time monitored capacitance and transconductance. The currents flowing through the two current testers are expressed as follows: and ; in, It is the 90° phase current generated by a double-layer transistor under AC signal conditions; It is the 0° phase current from the gate drain to the source and drain; It is the 0° phase current from the drain to the source through the channel; A, B, C, and D represent the coefficients of the current in each part, and A+B=1, C+D=1, A=C, B=D; The expression for the current flowing through the two current meters is obtained. and Based on the obtained and The formulas for calculating capacitance and transconductance are as follows: Capacitor is represented as: ； Transconductance is represented as: ； Among them, C ox-ac It is a capacitor, ν ac It is alternating voltage, g m It is transconductance, and f is frequency.

6. The apparatus for testing the mobility of a double-layer transistor as described in claim 5, characterized in that, It also includes a processor that receives the current measured by the current tester and calculates the capacitance and transconductance based on the current value, and then calculates the linear mobility and saturation mobility based on the capacitance and transconductance.

7. The apparatus for testing the mobility of a double-layer transistor as described in claim 5, characterized in that, The current tester is a lock-in amplifier, which separates the DC component and the AC component.

8. The apparatus for testing the mobility of a double-layer transistor as described in claim 5, characterized in that, The double-layer transistor has an ionic liquid double layer and an oxide semiconductor active layer.

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