A total dose radiation induced leakage current modeling method for MOS transistors

Abstract

The present invention discloses a total dose radiation induced leakage current modeling method for MOS transistors. First, radiation data is generated, and then the current change ΔI caused by different total doses is calculated. D Calculate and adjust ΔI according to different working areas D Modeling, establishing a SPICE model containing MOS tubes and current sources, current simulation based on a simplified model, and error analysis. The advantage of the present invention is that a simplified model is established to achieve accurate simulation of the total dose effect off-state leakage current, further improving efficiency and reducing costs.

Description

Technical Field

[0001] The invention belongs to the technical field of radiation effects, and in particular relates to a total dose radiation induced leakage current modeling method. Background Art

[0002] At present, more and more electronic devices are used in radiation environments. High-energy particles cause radiation damage to devices, affecting the reliability of integrated circuits. The total dose effect is an important radiation damage effect. The accumulation of trapped charge will increase the off-state leakage current of the device, which also increases the power consumption of the integrated circuit, changes key parameters, and even causes functional failure. Therefore, how to simulate the total dose resistance of integrated circuits has become a major problem at present. The mechanism of radiation-induced off-state leakage current is complex, and its amplitude varies with device size, absorbed dose, drain voltage and substrate bias. Existing modeling and simulation methods mainly rely on data from ground irradiation tests and TCAD simulations.

[0003] Regarding the modeling of radiation-induced off-state leakage current, the literature [S. A. N. Solmaz and M.B.Yelten, "Modeling of Total Ionizing Dose Degradation on 180-nm n-MOSFETs Using BSIM3," in IEEE Transactions on Electron Devices, vol. 66, no. 11, pp. 4617-4622, Nov. 2019, doi: 10.1109 / TED.2019.2926931] proposed an approach to convert the total ionizing dose experimental test or TCAD simulation data on the gate-source voltage V GS The off-state leakage current value when V is 0V is used as the fixed current source amplitude, and the current source is added to the circuit for simulation. GS As the off-state leakage current increases, the method does not take this phenomenon into account. GS When the voltage is between 0V and the threshold voltage, the estimated off-state leakage current is too small.

[0004] The literature [ISEsqueda, HJBarnaby and MLAlles, "Two-dimensional methodology for modeling radiation-induced off-state leakage in CMOS technologies," in IEEE Transactions on Nuclear Science, vol. 52, no. 6, pp. 2259-2264, Dec. 2005, doi: 10.1109 / TNS.2005.860671.] proposed a two-dimensional device simulation method to model the off-state leakage current of MOS tubes. The idea of ​​modeling is to model the off-state leakage current as a parasitic MOS transistor generated at the edge of the STI, and the total off-state leakage current is the sum of the leakage currents of all parasitic MOS transistors. The effective channel length and width, effective mobility, and effective threshold voltage of the parasitic MOS transistor are determined by the gate bias voltage and the oxide charge density captured in the STI. Finally, the parameters are merged into the circuit model for simulation, and the leakage current of the parasitic MOS transistor is calculated. However, it is very difficult to obtain the above parameters from the TCAD two-dimensional device model, and the modeling process is complicated and costly.

[0005] In view of the problems existing in the above work, it is very necessary to establish a simplified model to realize the accurate simulation of the total dose effect off-state leakage current, further improve the efficiency and reduce the cost. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art, the present invention provides a total dose radiation induced leakage current modeling method for MOS transistors. First, radiation data is generated, and then the current change ΔI caused by different total doses is calculated. D Calculate and adjust ΔI according to different working areas D Modeling, establishing a SPICE model containing MOS tubes and current sources, current simulation based on a simplified model, and error analysis. The advantage of the present invention is that a simplified model is established to achieve accurate simulation of the total dose effect off-state leakage current, further improving efficiency and reducing costs.

[0007] The technical solution adopted by the present invention to solve the technical problem includes the following steps:

[0008] Step 1: Obtain current and voltage data before and after total dose irradiation, and at different total doses;

[0009] Step 2: I D -V GS Data and unirradiated I D -V GSThe curve data is subtracted to obtain the I caused by the total dose effect D -V GS Curve change ΔI D , as shown in formula (1):

[0010] I D (rad)=I D (prerad)+ΔI D (1)

[0011] Where ΔI D I is the total dose effect D -V GS Curve change, I D (prerad) is the leakage current before irradiation, I D (rad) is the leakage current after irradiation;

[0012] Step 3: According to the semiconductor physical model, ΔI D The model is divided into three regions: weak inversion region, strong inversion region and velocity saturation region. D -V GS The formulas are shown in (2)(3)(4) respectively.

[0013]

[0014]

[0015]

[0016] Among them, I DSwi Represents the weak inversion region current of the transistor, I DSsi represents the strong inversion region current of the transistor, u represents the carrier mobility, I DSvs Represents the transistor speed saturation current, V GS is the gate-source voltage, V T is the threshold voltage, It represents the transition point between the weak inversion region and the strong inversion region. It represents the transition point between the strong inversion region and the speed saturation region. The factor n is related to the bias voltage. Between 70mV and 80mV, v sat is the saturation rate, C ox is the gate oxide capacitance per unit area, μ is the mobility, W and L represent the device size, I D0 is the characteristic current, nkT / q represents the proportionality factor, k is the Boltzmann constant, and q is the electron charge;

[0017] For ΔI D The modeling is based on the double exponential model in the weak inversion region, the linear function model in the strong inversion region, and the ΔI in the velocity saturation region.D The mean value in the area;

[0018] Step 4: ΔI D After the modeling is completed, ΔI D The model is described in Verilog-A, and ΔI D Considered as a current source controlled by the gate-source voltage and the total dose, the current source is connected in parallel with the transistor;

[0019] Step 5: Add the MOS tube current and the current source current to represent the leakage current after total dose irradiation, and implement total dose effect leakage current simulation based on the simplified model in Spectre;

[0020] Step 6: Perform error analysis; calculate I in the Spectre simulator D -V GS Curve and I of TCAD under corresponding irradiation dose D -V GS If the error is within the allowable range, ΔI is accepted. D Modeling; otherwise, repeat the fitting process, correct the fitting parameters of the weak inversion region, strong inversion region, and velocity saturation, and re-model the model.

[0021] Preferably, the method of obtaining the current and voltage data in step 1 includes TCAD total dose simulation or ground total dose experiment.

[0022] Preferably, the The typical value is 5L.

[0023] The beneficial effects of the present invention are as follows:

[0024] The total dose radiation induced leakage current modeling method of the MOS transistor proposed in the present invention realizes the simulation of the off-state leakage current in the spectre simulator with the help of a simplified model, and is suitable for the leakage current modeling of the weak inversion region, strong inversion region, and speed saturation of the MOS tube; at the same time, it can realize the radiation induced leakage current simulation under any total dose, reduce the cost of the total dose effect simulation, and shorten the time for evaluating the radiation resistance of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart for modeling total dose radiation induced leakage current of MOS transistors of the present invention.

[0026] Figure 2 The present invention ΔI D Modeling schematic.

[0027] Figure 3 I after TCAD simulation of total dose irradiation in the embodiment of the present invention D -VGS curve.

[0028] Figure 4 I after SPICE simulation of total dose irradiation in the embodiment of the present invention D -V GS curve.

[0029] Figure 5 This is the TCAD and SPICE off-state leakage current error at 500 krad in the embodiment of the present invention.

[0030] Figure 6 It is the maximum error of off-state leakage current of TCAD and SPICE under 100krad-500krad of the embodiment of the present invention.

[0031] Figure 7 This is the three-dimensional structure of the 0.18μm NMOS device according to an embodiment of the present invention.

[0032] Figure 8 is the ΔI after the total dose irradiation of the embodiment of the present invention D curve.

[0033] Fig. 9 It is a schematic diagram of a Verilog-A model of an embodiment of the present invention.

[0034] Fig.10 ΔI is the embodiment of the present invention D Spectre simulation results. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0036] The purpose of the present invention is to accurately model the radiation-induced off-state leakage current of MOS transistors. The model is built by dividing the change in the transfer characteristic curve caused by the total dose effect into three regions: weak inversion region, strong inversion region, and speed saturation region. The model is implemented using Verilog-A and finally integrated into the Spectre simulator to complete the leakage current simulation evaluation of analog and digital integrated circuits.

[0037] The flow chart of the total dose radiation induced leakage current modeling method of the MOS transistor provided by the present invention is as follows: Figure 1 .

[0038] The specific modeling steps are as follows:

[0039] Step 1: Obtain current and voltage data before and after total dose irradiation, as well as at different total doses. Data acquisition methods include TCAD total dose simulation or ground total dose experiment.

[0040] Step 2: I under different total doses D -V GSData and unirradiated I D -V GS The curve data is subtracted to obtain the I caused by the total dose effect D -V GS Curve change ΔI D , as shown in formula (1).

[0041] I D (rad)=I D (prerad)+ΔI D (1)

[0042] Where ΔI D I is the total dose effect D -V GS Curve change, I D (prerad) is the leakage current before irradiation, I D (rad) is the leakage current after irradiation.

[0043] Step 3: According to the semiconductor physics model, ΔI D The model is divided into three regions: weak inversion region, strong inversion region and velocity saturation region. D -V GS The formulas are shown in (2)(3)(4) respectively.

[0044]

[0045]

[0046]

[0047] Among them, V GS is the gate-source voltage, V T is the threshold voltage, It represents the transition point between the weak inversion region and the strong inversion region. It represents the transition point between the strong inversion region and the speed saturation region. The factor n is related to the bias voltage. About 70mV to 80mV, v sat is the saturation rate, C ox is the gate oxide capacitance per unit area, μ is the mobility, The typical value is 5L. W and L represent the device size, I D0 is the characteristic current, nkT / q represents the proportionality factor, k is the Boltzmann constant, and q is the electron charge. D In the weak inversion region, a double exponential model is used to simulate the phenomenon that as the total dose increases, the off-state leakage current amplitude increases, the leakage current change slows down, and the leakage current platform is extended. In the strong inversion region, a linear function model is used to approximate. In the speed saturation region, ΔI DThe average value in this area.

[0048] Step 4: ΔI D After the modeling is completed, ΔI D The model is described in Verilog-A, and ΔI D Considered as a current source controlled by the gate-source voltage and the total dose, the current source is connected in parallel with the transistor, such as Figure 2 shown.

[0049] Step 5: Add the MOS tube current and the current source current to get the leakage current after total dose irradiation, and implement total dose effect leakage current simulation based on a simplified model in Spectre.

[0050] Step 6: Perform error analysis. Calculate I in the Spectre simulator D -V GS Curve and I of TCAD under corresponding irradiation dose D -V GS If the error of the curve is within the allowable range, the modeling is acceptable. Otherwise, adjust the fitting functions of the weak inversion region, strong inversion region, and velocity saturation, and re-model the model.

[0051] The key point of the present invention is that the total dose radiation induced leakage current modeling method of the MOS transistor is proposed by calculating the I of the three regions of weak inversion region, strong inversion region and speed saturation region. D -V GS The curve variation modeling can reproduce the TCAD total dose leakage current simulation curve in the Spectre simulation environment. By writing the Verilog-A model, the simulation of radiation-induced off-state leakage current can be integrated into the standard ASIC design process.

[0052] The size of the NMOS tube simulated in the present invention is 0.22μm / 0.18μm, and the ΔI D The model was modeled and implemented in the Spectre simulator in the form of Verilog-A. The total dose effect simulation of the NMOS tube was performed by TCAD and the leakage current modeling simulation by SPICE, and the I D -V GS Curve like Figure 3 and Figure 4 shown.

[0053] When TID=500krad, at V GS The error between the SPICE simulation result in the present invention and the TCAD total dose simulation result is calculated according to formula (5) in the range of 0V-1.8V, I D,TCAD Represents TCAD simulation I under a certain dose D -VGS Curve, I D,SPICE Indicates SPICE simulation I under a certain dose D -V GS Curve, error results such as Figure 5 As shown in the figure. In the case of 500krad, the maximum error value is 25.61%, and only one point is higher than 20%, and the error values ​​of most points are lower than 10%. The maximum error under different doses is shown in the figure. Figure 6 As shown, the error distribution at each dose is similar Figure 5 , the error values ​​of most points are less than 10%, due to TCAD 3D device modeling and ΔI D The error in the fitting process leads to a few points with error values ​​greater than 20%.

[0054]

[0055] Example:

[0056] The flow chart of the present invention is as follows Figure 1 The device selected in the present invention is a 0.18μm process NMOS tube of Foundry A, with a size of 0.22μm / 0.18μm. First, based on the TCAD of Company B, a three-dimensional structure modeling of the NMOS device is performed, as shown in FIG. Figure 7 After the modeling is completed, the electrical characteristics of the structure are simulated in the unirradiated state, the current-voltage curve is obtained, and the model is calibrated according to the SPICE simulation data to ensure that the model can be used for the subsequent total dose effect simulation.

[0057] After the model calibration is completed, the TCAD total dose effect simulation is performed. The device electrode bias state is set to the on state during irradiation, and the device bias state is set to V after irradiation. D =0.1V, V G Scan from 0 to 1.8 V. Set the irradiation dose rate and different simulation times to achieve a total dose range of 100krad-500krad, and finally obtain ΔI under different total doses D Curves, such as Figure 8 shown.

[0058] Next, ΔI D In the weak inversion region, a double exponential function is used to fit ΔI D , as shown in formula (6); in the strong inversion region, a linear function fitting is used, as shown in formula (7); in the velocity saturation region, a straight line fitting is used, as shown in formula (8).

[0059] ΔI D,wi (V GS )=k1 exp(k2V GS )+k3 exp(k4V GS) (6)

[0060] ΔI D,si (V GS )=k5V GS +k6 (7)

[0061] ΔI D,vs (V GS )=k7 (8)

[0062] After the fitting is completed, the relationship between the model parameters k1-k7 and the total dose is modeled, and the parameters k1-k7 are regarded as functions of the total dose, as shown in formula (9).

[0063] k i =f i (D) (9)

[0064] Among them, k1, k2, k3 have an exponential relationship with the total dose, k4, k6, k7 have a linear function relationship with the total dose, and k5 is a constant. The modeling relationship between parameter k and the total dose is shown in formulas (10)-(17).

[0065] k1=1.059×10 -8 exp(0.0068D) (10)

[0066] k2=-175.4exp(-0.01582D) (11)

[0067] k3=1.737×10 -10 exp(0.007414D) (13)

[0068] k4=-0.0124D+17.97 (14)

[0069] k5=1.4593×10 -6 (15)

[0070] k6=7.312×10 -12 D 2 -2.608×10 -9 D (16)

[0071] k7=3.43×10 -9 D+5.688×10 -8 (17)

[0072] The value of k5 in formula (15) is the average value of k5 under different total doses.

[0073] ΔI D After the modeling is completed, the model is described in Verilog-A and added to the simulator for circuit simulation calls. Fig. 9As shown, the Verilog-A model contains three terminals connected to the gate, drain, and source of the MOS tube. This model obtains the NMOS tube V GS Voltage calculation to get ΔI D ,like Fig.10 As shown. D Applied to the source and drain terminals of the MOS tube to achieve current parallel connection, the leakage current after irradiation is finally obtained as Figure 4 shown.

Claims

1. A total dose radiation induced leakage current modeling method for MOS transistors, characterized in that: The steps include: Step 1: Obtain current and voltage data before and after total dose irradiation, and at different total doses; Step 2: I D -V GS Data and unirradiated I D -V GS The curve data is subtracted to obtain the I caused by the total dose effect. D -V GS Curve change ΔI D , as shown in formula (1): AND D (work)=I D (processing)+ΔI D (1) Where ΔI D I is the total dose effect D -V GS Curve change, I D (prerad) is the leakage current before irradiation, I D (rad) is the leakage current after irradiation; Step 3: According to the semiconductor physical model, ΔI D The model is divided into three regions: weak inversion region, strong inversion region and velocity saturation region. D -V GS The formulas are shown in (2)(3)(4) respectively; Among them, I DSwi Represents the weak inversion region current of the transistor, I DSsi represents the strong inversion region current of the transistor, u represents the carrier mobility, I DSvs Represents the transistor speed saturation current, V GS is the gate-source voltage, V T is the threshold voltage, It represents the transition point between the weak inversion region and the strong inversion region. It represents the transition point between the strong inversion region and the speed saturation region. The factor n is related to the bias voltage. Between 70mV and 80mV, v sat is the saturation rate, C ox is the gate oxide capacitance per unit area, μ is the mobility, W and L represent the device size, I D0 is the characteristic current, nkT / q represents the proportionality factor, k is the Boltzmann constant, and q is the electron charge; For ΔI D The modeling is based on the double exponential model in the weak inversion region, the linear function model in the strong inversion region, and the ΔI in the velocity saturation region. D The mean value in the area; Step 4: ΔI D After the modeling is completed, ΔI D The model is described in Verilog-A, and ΔI D Considered as a current source controlled by the gate-source voltage and the total dose, the current source is connected in parallel with the transistor; Step 5: Add the MOS tube current and the current source current to represent the leakage current after total dose irradiation, and implement total dose effect leakage current simulation based on the simplified model in Spectre; Step 6: Perform error analysis; calculate I in the Spectre simulator D -V GS Curve and I of TCAD under corresponding irradiation dose D -V GS If the error is within the allowable range, ΔI is accepted. D Modeling; otherwise, repeat the fitting process, correct the fitting parameters of the weak inversion region, strong inversion region, and velocity saturation, and re-model the model.

2. A total dose radiation induced leakage current modeling method for a MOS transistor according to claim 1, characterized in that: The method of obtaining the current and voltage data in step 1 includes TCAD total dose simulation or ground total dose experiment.

3. The total dose radiation induced leakage current modeling method of a MOS transistor according to claim 1, characterized in that: Said The typical value is 5L.

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