CN112699628B - OTS + PCM unit simulation system of three-dimensional phase change memory - Google Patents

Abstract

The invention discloses an OTS + PCM unit simulation system of a three-dimensional phase change memory, wherein an I-V module of a PCM unit constructs an I-V characteristic model of the OTS + PCM unit based on a P-F model and an ohm law, and after the I-V module of the OTS + PCM unit receives current or voltage excitation applied from the outside, the excitation applied from the outside and the non-crystallization rate of the PCM unit are brought into the I-V characteristic model of the OTS + PCM unit, and the current and the voltage on the PCM unit are obtained through calculation; the PCM temperature module calculates the temperature of the PCM unit in real time by adopting a thermal resistance and thermal capacitance (RC) network according to the current and the voltage on the PCM unit; the PCM phase change module judges whether the PCM unit is in a crystallization state or an amorphization state according to the temperature of the PCM unit, calculates the crystallization rate and the amorphization rate of the PCM unit, takes the sum of the crystallization rate and the amorphization rate as a real-time phase change rate, calculates the amorphization rate of the PCM unit according to the obtained real-time phase change rate, and outputs the amorphization rate to the PCM unit I-V module. The invention can directly operate the model by adopting current and voltage excitation, ensure the accuracy and accurately simulate the OTS + PCM unit.

Description

An OTS+PCM cell simulation system for three-dimensional phase change memory

technical field

The invention belongs to the technical field of microelectronics, and more particularly, relates to an OTS+PCM unit simulation system of a three-dimensional phase change memory.

Background technique

Phase change memory is a kind of non-volatile memory developed by utilizing the characteristics of phase change materials that can be rapidly and repeatedly converted between crystalline and amorphous states, and different states have huge differences in properties. The advantages of process integration, high density, low cost and non-volatile are considered to be the most promising devices for the next generation of non-volatile memory. However, in order to solve the leakage current problem of the crossbar structure storage array of the phase change memory, the researchers used the OTS gate tube with a similar process to the phase change memory to configure the device of the 1S1R structure. Compared with other gate devices, the It has the advantages of simple structure, 3-dimensional stackability, fast on/off time and high durability. For the successful commercial application of 3D phase change memory, good chip circuit design is very important. The input files of circuit simulation software generally include circuit structure description files and component model files, which constitute the overall circuit model system. Therefore, an OTS+PCM cell simulation system that can accurately construct a three-dimensional phase-change memory with electrical characteristics is very important for the circuit design of a phase-change memory chip.

There are many researches on SPICE simulation system of 3D phase change memory OTS+PCM unit, SPICE model system of separate OTS unit or PCM unit, but there are few model systems integrating OTS+PCM unit. The SPICE model system of the PCM unit is usually composed of three parts: the electrical module, the temperature module and the crystallization module, and the OTS in the model system of the OTS+PCM unit usually adopts the same model as the electrical module in the PCM unit model system. Both the OTS unit and the PCM unit show an S-shaped curve under current excitation. The existing model cannot directly use current and voltage excitation at the same time without guaranteeing accuracy. However, the actual operation of the OTS+PCM unit usually uses current excitation for erasing Write, voltage excitation to read. Therefore, it cannot be applied to actual chip design.

SUMMARY OF THE INVENTION

In view of the above defects or improvement requirements of the prior art, the present invention provides an OTS+PCM cell simulation system of a three-dimensional phase change memory, which aims to solve the problem that the prior art cannot accurately simulate the OTS+PCM cell.

In order to achieve the above object, the present invention provides an OTS+PCM unit simulation system of a three-dimensional phase change memory, including: an OTS unit I-V module, a PCM unit I-V module, a PCM temperature module and a PCM phase change module; wherein, the OTS unit I-V module It is connected in series with the PCM unit I-V module to form an OTS+PCM unit I-V module; the OTS+PCM unit includes the OTS unit and the PCM unit connected in series;

The PCM unit I-V module is used to construct the OTS+PCM unit I-V characteristic model based on the P-F model and Ohm's law. Enter the OTS+PCM unit I-V characteristic model, calculate the current and voltage on the PCM unit, and output them to the PCM temperature module; among them, the external excitation is current or voltage; when the external excitation is voltage, the OTS unit The I-V module is used to limit the current of the PCM unit I-V module;

The PCM temperature module is used to calculate the temperature of the PCM unit in real time according to the current and voltage on the PCM unit, using the thermal resistance and heat capacity RC network, and output it to the PCM phase change module;

The PCM phase change module is used to judge whether the PCM unit is in a crystalline state or an amorphized state according to the temperature of the PCM unit, calculate the crystallization rate and amorphization rate of the PCM unit, and use the sum of the two as the real-time phase change rate. The obtained real-time phase transition rate calculates the amorphization rate of the PCM cell and outputs it to the PCM cell I-V module.

Further preferably, the above-mentioned OTS+PCM unit I-V characteristic model is:

I _OTS =I ₁ +(-I ₁ +I _on1 F _th )F _h

I ₁ =2qA(dz/t ₀ )N _t exp(-E _t /kT ₀ )sinh(V _OTS dz/(2kT ₀ u _a ))

I _on1 =(V _OTS -V _h1 )/R _on1

I _PCM =I ₂ +(-I ₂ +I _on2 )F _th

I ₂ =(exp(K(C _a )V _PCM )-1)/(K(C _a )R(C _a ))

I _on2 =(V _PCM -V _h2 )/R _on2

R(C _a )=R _a C _a +R _on2 (1-C _a )

Among them, I _OTS is the current on the OTS unit, I ₁ is the high resistance state current of the OTS unit, I _on1 is the low resistance state current of the OTS unit, q is the amount of charge, A is the cross-sectional area of the OTS unit, and dz is the trap The average distance between the two, t ₀ is the characteristic escape time of bound electrons, N _t is the total trap electron concentration, E _t is the distance between the deep trap and the shallow trap, k is the Boltzmann constant, T ₀ is the ambient temperature, u _a is the thickness of the OTS cell, V _OTS is the voltage on the OTS cell, V _h1 is the holding voltage of the OTS cell, R _on1 is the on-state resistance of the OTS cell, I _PCM is the current on the PCM cell, and I ₂ is the PCM cell’s High resistance state current, I _on2 is the low resistance state current of the PCM cell, K(C _a ) is the corresponding fitting coefficient when the amorphization rate of the PCM cell is _Ca , _Ca is the amorphization rate, V _PCM is the voltage on the PCM cell, R(C _a ) is the resistance value of the PCM cell when the amorphization rate of the PCM cell is _Ca , V _h2 is the holding voltage of the PCM cell, and R _on2 is the on-state resistance of the PCM cell , I is the externally applied current received by the OTS+PCM unit IV module, V is the externally applied voltage received by the OTS+PCM unit IV module; I _th is the preset current threshold, V _th is the preset voltage threshold, α is the proportional coefficient;

If the external excitation is the voltage V, V=V _OTS +V _PCM ;

If the external excitation is the current I, I=I _OTS =I _PCM .

Further preferably, the temperature expression of the PCM unit is:

Among them, I _PCM is the current on the PCM cell, V _PCM is the voltage across the PCM cell, T is the temperature of the PCM cell, T ₀ is the ambient temperature, r _tb is the lower electrode thermal resistance, r _tgst is the PCM cell thermal resistance, r _tt is the thermal resistance of the upper electrode, C _t is the heat capacity of the PCM cell, and t is the time.

Further preferably, the temperature of the PCM unit is compared with the melting point and crystallization temperature of the phase change material of the PCM unit; if the temperature of the PCM unit is higher than the melting point of the phase change material, the PCM unit is in an amorphous state, and at this time, the crystal of the PCM unit is in an amorphous state. If the temperature of the PCM unit is lower than the melting point of the phase change material and higher than the crystallization temperature, the PCM unit is in a crystalline state, and at this time, the amorphization rate of the PCM unit is 0.

Further preferably, the above-mentioned real-time phase change rate is:

V _a =V _ac F _c F _ac +V _aa F _aa ,

T_c为晶化温度，T_a为熔点温度，α为比例系数。where V _ac is the crystallization rate, V _aa is the amorphization rate,

T _c is the crystallization temperature, Ta is the melting point temperature, and _α is the proportionality coefficient.

Further preferably, the above-mentioned crystallization rate is obtained by calculating the sum of the nucleation rate and the growth rate based on the nucleation-growth theory according to the temperature of the PCM unit.

Further preferably, the above-mentioned amorphization rate V _aa =a(TT _m )/h ₁ r _ta ; wherein, T is the temperature of the PCM unit, T _m is the melting point of the phase change layer of the PCM unit, and h ₁ is the melting point of the PCM unit Latent heat, r _ta is the thermal resistance of the amorphized region of the PCM cell, and a is the scaling factor.

In general, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

1. The present invention provides an OTS+PCM unit simulation system of a three-dimensional phase change memory, wherein the PCM unit I-V module constructs an OTS+PCM unit I-V characteristic model based on the P-F model and Ohm's law. When the OTS+PCM unit I-V module receives the After the external excitation, the external excitation and the amorphization rate of the PCM unit are brought into the I-V characteristic model of the OTS+PCM unit, and the current and voltage on the PCM unit are calculated. Compared with the prior art, it can be used simultaneously. The current and voltage excitation operates directly on the model and ensures its accuracy, which can accurately simulate the OTS+PCM unit.

2. The OTS+PCM unit simulation system of the three-dimensional phase change memory provided by the present invention divides the I-V module of the OTS unit into two sections: a high-resistance state segment and a low-resistance state segment. The high-resistance state segment is derived from the P-F model. The carrier transport model of the PCM unit is also used to retain the holding voltage of the OTS, so that the electrical I-V characteristics of the OTS unit can be more accurately simulated; the PCM unit I-V module also divides it into two sections, but Different from the model selected for the high resistance state of the OTS cell, the simplified P-F model selected for the PCM cell can simulate various partially crystalline and fully crystalline and fully amorphous states with an amorphization ratio of 0 to 1, and then The threshold current and the holding current are ignored to ensure that it can complete the erasing and writing operations under the current excitation. Because the I-V module of the OTS unit and the I-V module of the PCM unit adopt a segmented model, they can be read, erased and written accurately under voltage excitation. Under current excitation, since the OTS unit and the PCM unit are connected in series, it is equivalent to operating the PCM unit independently, so the current erasing and writing operation can be performed on it. And under the joint action of the temperature module and the phase change module of the PCM unit, it can accurately simulate the change of the amorphization ratio of the PCM unit under a single pulse or pulse sequence, which can provide a reliable reference for the design of the peripheral circuit of the chip and the neuron. Therefore, it can greatly improve the efficiency and accuracy of chip design and shorten the product design cycle.

Description of drawings

1 is a schematic structural diagram of an OTS+PCM cell simulation system of a three-dimensional phase change memory provided by the present invention;

2 is a schematic diagram of a DC I-V curve obtained by performing a voltage scan to the OTS+PCM unit simulation system provided by the present invention;

3 is a schematic diagram of the RI curve of the PCM unit obtained by applying a pulse sequence to the OTS+PCM unit simulation system provided by the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

In order to achieve the above object, the present invention provides an OTS+PCM unit simulation system of a three-dimensional phase change memory, as shown in FIG. Variable module 4; wherein, the OTS unit I-V module 1 and the PCM unit I-V module 2 are connected in series to form an OTS+PCM unit I-V module; the OTS+PCM unit includes an OTS unit and a PCM unit connected in series;

The PCM unit I-V module 1 is used to construct the OTS+PCM unit I-V characteristic model based on the P-F model and Ohm's law. Bring it into the I-V characteristic model of the OTS+PCM unit, calculate the current and voltage on the PCM unit, and output them to the PCM temperature module 3; among them, the external excitation is current or voltage; when the external excitation is voltage, The OTS unit I-V module 2 is used to limit the current of the PCM unit I-V module 1;

Specifically, the above process of constructing the I-V characteristic model of the OTS+PCM unit based on the P-F model and Ohm's law is as follows:

The OTS+PCM unit includes the OTS unit and the PCM unit connected in series; the DC I-V characteristics of the OTS unit and the PCM unit are analyzed respectively. For an OTS cell, when it is in a low-resistance state, its I-V characteristics conform to Ohm's law because its mobility does not change, similar to metal behavior. When it is in a high resistance state, the current changes exponentially with the voltage, and this change is often described as the P-F model. However, in the DC I-V characteristics of the OTS unit, in addition to the two steady-state stages of the high-resistance state and the low-resistance state, there is also a transition characteristic in which the voltage decreases with the increase of the current after the threshold voltage, which is called S shape negative differential characteristic, but this I-V characteristic is unstable, and will only be captured in the DC I-V test when the excitation is current. In fact, the actual erasing and writing operations of the OTS+PCM cells will not take advantage of this feature regardless of whether they use voltage or current, and the read operation generally adopts voltage control. To limit leakage current in the array, the unselected OTS cell strobes will be biased in the off state (high impedance state), and the selected OTS cell strobes will be biased in the on state (low impedance state) ) to achieve sufficient access voltage drop across the target memory cell. Therefore, the steady-state characteristics of the OTS strobes actually in the 3D phase change memory are more important than the switching, which determines the performance of the array. Therefore, the conversion characteristic of the S-shaped negative differential characteristic is ignored here, and the step function is used to combine the I-V of the two steady-state characteristics.

For the PCM unit, since both the PCM unit and the OTS unit are made of chalcogenide materials, they are similar in structure and material, so the DC I-V characteristics of the PCM unit are similar to the DC I-V characteristics of the OTS unit. The low resistance state of the PCM unit The DC I-V characteristics also use Ohm's law; the high-resistance DC I-V of the PCM unit is also calculated by the P-F model. Therefore, the P-F model is simplified to represent the high-impedance DC I-V characteristics of the PCM cell.

After analyzing the DC I-V characteristics of the PCM unit and the OTS unit, the step function is used to combine the DC I-V of the PCM unit and the OTS unit at different stages, and the I-V characteristic model of the OTS+PCM unit is obtained:

I _OTS =I ₁ +(-I ₁ +I _on1 F _th )F _h

I ₁ =2qA(dz/t ₀ )N _t exp(-E _t /kT ₀ )sinh(V _OTS dz/(2kT ₀ u _a ))

I _on1 =(V _OTS -V _h1 )/R _on1

I _PCM =I ₂ +(-I ₂ +I _on2 )F _th

I ₂ =(exp(K(C _a )V _PCM )-1)/(K(C _a )R(C _a ))

I _on2 =(V _PCM -V _h2 )/R _on2

R(C _a )=R _a C _a +R _on2 (1-C _a )

Among them, I _OTS is the current on the OTS unit, I ₁ is the high resistance state current of the OTS unit, I _on1 is the low resistance state current of the OTS unit, q is the amount of charge, A is the cross-sectional area of the OTS unit, and dz is the trap The average distance between the two, t ₀ is the characteristic escape time of bound electrons, N _t is the total trap electron concentration, E _t is the distance between the deep trap and the shallow trap, k is the Boltzmann constant, T ₀ is the ambient temperature, u _a is the thickness of the OTS cell, V _OTS is the voltage on the OTS cell, V _h1 is the holding voltage of the OTS cell, R _on1 is the on-state resistance of the OTS cell, I _PCM is the current on the PCM cell, and I ₂ is the PCM cell’s High resistance state current, I _on2 is the low resistance state current of the PCM cell, K(C _a ) is the corresponding fitting coefficient when the amorphization rate of the PCM cell is _Ca , _Ca is the amorphization rate, V _PCM is the voltage on the PCM cell, R(C _a ) is the resistance value of the PCM cell when the amorphization rate of the PCM cell is _Ca , V _h2 is the holding voltage of the PCM cell, and R _on2 is the on-state resistance of the PCM cell , I is the externally applied current received by the OTS+PCM unit IV module, V is the externally applied voltage received by the OTS+PCM unit IV module; I _th is the preset current threshold, V _th is the preset voltage threshold, α is the proportional coefficient;

If the external excitation is the voltage V, V=V _OTS +V _PCM ;

If the external excitation is the current I, I=I _OTS =I _PCM .

The PCM temperature module 3 is used to calculate the temperature of the PCM unit in real time according to the current and voltage on the PCM unit using the thermal resistance and heat capacity RC network, and output it to the PCM phase change module 4; The RC network is used to calculate the highest point temperature of the PCM unit during the pulse signal period with the ambient temperature as the initial condition. It can also simulate the continuously applied pulse sequence, and the ambient temperature is updated to the real-time temperature at the end of each pulse;

The temperature of the PCM unit is related to the Joule heat generated by the current resistance under excitation, the heat dissipation of the unit thermal resistance, the heat capacity, and the ambient temperature. It is not realistic to calculate the temperature of all points of the PCM cell, and the finite element analysis shows that the highest point of the temperature of the PCM cell is mainly concentrated in the PCM cell and the lower electrode area during the operation under the T-shaped structure, so in the simplified calculation, only the highest point is calculated. Temperature, the present invention adopts the method of thermoelectric analogy to calculate the highest point temperature through an RC circuit composed of thermal resistance and thermal capacitance. Therefore, the calculation expression of the temperature calculation module to simulate the temperature of the PCM unit is:

Among them, I _PCM is the current on the PCM cell, V _PCM is the voltage across the PCM cell, T is the temperature of the PCM cell, T ₀ is the ambient temperature, r _tb is the lower electrode thermal resistance, r _tgst is the PCM cell thermal resistance, r _tt is the thermal resistance of the upper electrode, C _t is the heat capacity of the PCM cell, and t is the time.

Specifically, the formula for calculating the thermal resistance of the PCM unit is:

The formula for calculating the heat capacity of the PCM unit is:

C _t =τ/[1/r _tb +1/(r _tgst +r _tt )]

Among them, _Ca is the amorphization rate of the PCM unit, d _gst is the thickness of the PCM unit, S is the contact area between the lower electrode and the PCM unit, and _ka and k _c are the heat of the PCM unit in the amorphous and crystalline states, respectively. conductivity, and τ is the thermal time constant.

The PCM phase change module 4 is used in the PCM phase change module to determine whether the PCM unit is in a crystalline state or an amorphized state according to the temperature of the PCM unit, calculate the crystallization rate and amorphization rate of the PCM unit, and use the sum of the two as the Real-time phase change rate, and calculate the amorphization rate of the PCM unit according to the obtained real-time phase change rate, and output it to the PCM unit I-V module.

Specifically, the temperature of the PCM unit is compared with the melting point and crystallization temperature of the phase change material of the PCM unit; if the temperature of the PCM unit is higher than the melting point of the phase change material, the PCM unit is in an amorphous state, and at this time, the crystallization of the PCM unit The rate is 0; if the temperature of the PCM unit is lower than the melting point of the phase change material and higher than the crystallization temperature, the PCM unit is in a crystalline state, at this time, the amorphization rate of the PCM unit is 0; calculate the crystallization rate of the PCM unit and The amorphization rate is calculated, and the sum of the two is taken as the real-time phase transition rate, and the amorphization rate of the PCM unit is calculated according to the obtained real-time phase transition rate, and is output to the PCM unit I-V module.

Further, the PCM phase change module includes a phase change rate calculation circuit and a capacitor; wherein, the phase change rate calculation circuit is used to calculate the crystallization rate and amorphization rate of the PCM unit, and the sum of the two is used as the real-time phase change rate, Output to the capacitor; the capacitor is used to integrate the real-time phase transition rate and calculate the amorphization rate.

Specifically, the crystallization rate is the change in the volume of the PCM unit that is crystallized in unit time; according to the temperature of the PCM unit, based on the nucleation-growth theory, the sum of the nucleation rate and the growth rate is calculated to obtain the crystallization rate;

Specifically, the formula for calculating the crystallization rate is:

V _ac =-(P _n V _n V _a /V _m +S _a V _g ),

f=exp[-0.8/(1-T/T _m )]

Among them, P _n is the nucleation probability per unit time, V _n is the nucleation volume, Va is the volume of the amorphized region, V _m is the molecular volume of the phase change material, and _Sa is the difference between the _amorphized region and the crystalline region. interfacial area, V _g is the growth rate; α is the frequency factor of atomic vibration, E _a1 is the nucleation activation energy, γ is the excess free energy per unit area, ΔG is the excess Gibbs free energy, k _B is Boltzmann constant, T is the temperature of the PCM cell; C _a is the amorphization rate of the PCM cell, d _gst is the thickness of the PCM cell, f is the growth mode factor, a ₀ is the atomic transition distance, E _a2 is the atomic scattering activation energy; T _m is the melting point of the phase change layer of the PCM cell, and h ₁ is the latent heat of fusion of the PCM cell material.

The amorphization rate is the change in the volume of the amorphized PCM unit in unit time; specifically, the calculation formula of the amorphization rate is: V _aa =a(TT _m )/h ₁ r _ta ; where a is the ratio coefficient, T is the temperature of the PCM unit, T _m is the melting point of the phase change layer of the PCM unit, h ₁ is the latent heat of fusion of the PCM unit, r _ta is the thermal resistance of the amorphized region of the PCM unit, specifically, r _ta =C _{a d gst} /Ska , _Ca is the amorphization rate of the PCM cell, d _gst is the thickness of the PCM cell, S is the contact area between the lower electrode and the PCM cell, and _ka is the thermal conductivity of the PCM in the amorphous state.

T_c为晶化温度，T_a为熔点温度，α为比例系数；然后把PCM单元体积作为电容，用于积分运算，得到PCM单元的非晶化率。其计算式为：

其中电容值

d_gst为PCM单元的厚度，t为时间。Further, according to the temperature of the PCM unit output by the PCM temperature module, it is determined whether the PCM unit is crystallized or amorphized. Here, a step function is used to calculate, and then the sum of the crystallization rate and the amorphization rate is used as the real-time phase transition rate. Specifically, is: V _a =V _ac F _c F _ac +V _aa F _aa , where V _ac is the crystallization rate, V _aa is the amorphization rate, and F _c , F _ac and F _aa are related to the crystallization temperature and melting point, respectively The step function of , which is used to determine whether crystallization or amorphization occurs; specifically,

T _c is the crystallization temperature, Ta is the melting point temperature, and α is the proportional coefficient; then the volume of the PCM unit is used as _a capacitance for integral operation to obtain the amorphization rate of the PCM unit. Its calculation formula is:

where capacitance value

d _gst is the thickness of the PCM cell and t is the time.

In order to further illustrate the accuracy of the OTS+PCM unit simulation system of the three-dimensional phase-change memory provided by the present invention, the following details are described in conjunction with experiments:

Apply voltage excitation at both ends of the OTS+PCM unit for simulation simulation, and also set the initial temperature to room temperature 300K. In the HSPICE simulation environment, the PCM unit is in the crystalline and amorphous states to perform the scanning range of 0~5V. Voltage scanning, the threshold voltage VtS of the OTS+PCM cell in the OTS+SET state is 2.7V, the threshold voltage in the OTS+RESET state is 3.7V, and the holding voltage is 2.4V, and the DC I-V curve shown in Figure 2 is obtained; among them, The square curve is the result obtained by the simulation of the simulation system (referred to as model) provided by the present invention, and the circular curve is the test result of the actual device (reference) in the reference. It can be seen that the two curves basically overlap, and this The threshold voltages VtS and VtR of the simulation system provided by the invention are within 0.1V of the actual test results in the literature, which confirms the accuracy of the simulation system provided by the invention.

Further, the transient analysis was performed in the HSPICE simulation environment, the initial temperature was set to 300K at room temperature, the initial amorphization ratio was 1, and a pulse sequence with a pulse width of 1000 ns was applied. The initial amplitude of the pulse is 120uA, and the pulse amplitude is gradually increased in increments of 5uA. Figure 3 shows the R-I curve of the PCM obtained by simulation. Since the change trend of the amorphization ratio is consistent with the resistance value, the resistance value is replaced by the amorphization ratio. After the current exceeds 0.13mA, the amorphization ratio of the PCM unit decreases; After the voltage exceeds 0.19mA, as the pulse amplitude gradually increases, the amorphization ratio of PCM no longer decreases, indicating that the heat generated by the current pulse at this time makes the temperature of the PCM cell close to or greater than the melting temperature. It can be observed in the figure that in the process of decreasing the amorphization ratio, the resistance value gradually changes, showing a multi-valued distribution, which is in line with the characteristics of the real device.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (7)

1. An OTS + PCM cell emulation system for a three-dimensional phase change memory, comprising: the OTS unit I-V module, the PCM temperature module and the PCM phase change module;

the OTS unit I-V module and the PCM unit I-V module are connected in series to form an OTS + PCM unit I-V module; the OTS + PCM unit comprises an OTS unit and a PCM unit which are connected in series;

the PCM unit I-V module is used for constructing an OTS + PCM unit I-V characteristic model based on a P-F model and an ohm law, after receiving externally applied excitation, the OTS + PCM unit I-V module brings the externally applied excitation and the non-crystallization rate of the PCM unit into the OTS + PCM unit I-V characteristic model, calculates current and voltage on the PCM unit and outputs the current and voltage to the PCM temperature module; wherein the externally applied excitation is current or voltage; when the externally applied excitation is voltage, the OTS unit I-V module is used for limiting the current of the PCM unit I-V module;

the PCM temperature module is used for calculating the temperature of the PCM unit in real time by adopting a thermal resistance and thermal capacitance (RC) network according to the current and the voltage on the PCM unit and outputting the temperature to the PCM phase change module;

the PCM phase change module is used for judging whether the PCM unit is in a crystallization state or an amorphization state according to the temperature of the PCM unit, calculating the crystallization rate and the amorphization rate of the PCM unit, taking the sum of the crystallization rate and the amorphization rate as a real-time phase change rate, calculating the amorphization rate of the PCM unit according to the obtained real-time phase change rate, and outputting the amorphization rate to the PCM unit I-V module.

2. The OTS + PCM cell simulation system of a three-dimensional phase change memory of claim 1, wherein the OTS + PCM cell I-V characteristic model is:

I_OTS＝I₁+(-I₁+I_on1F_th)F_h

I₁＝2qA(dz/t₀)N_texp(-E_t/kT₀)sinh(V_OTSdz/(2kT₀u_a))

I_on1＝(V_OTS-V_h1)/R_on1

I_PCM＝I₂+(-I₂+I_on2)F_th

I₂＝(exp(K(C_a)V_PCM)-1)/(K(C_a)R(C_a))

I_on2＝(V_PCM-V_h2)/R_on2

R(C_a)＝R_aC_a+R_on2(1-C_a)

wherein, I_OTSIs the current on the OTS cell, I₁Is a high resistance state current of the OTS cell, I_on1Is the low resistance state current of the OTS unit, q is the charge amount, A is the cross-sectional area of the OTS unit, dz is the average distance between traps, t₀Is the characteristic escape time of bound electrons, N_tAs total trap electron concentration, E_tIs the distance between the deep trap and the shallow trap, k is the Boltzmann constant, T₀Is the ambient temperature u_aThickness of OTS cell, V_OTSIs the voltage across the OTS cell, V_h1Is the holding voltage of OTS cell, R_on1Is the on-resistance of the OTS cell, I_PCMIs the current on the PCM cell, I₂Is a high resistance state current of the PCM cell, I_on2Is a low resistance state current of PCM cell, K (C)_a) When the amorphous rate of the PCM cell is C_aFitting coefficient, C, corresponding to time_aIs a rate of amorphization, V_PCMIs the voltage across the PCM cell, R (C)_a) When the amorphous rate of the PCM cell is C_aResistance value of time PCM cell, V_h2Is the holding voltage of the PCM cell, R_on2The on-state resistance of the PCM unit, I is the current applied from the outside received by the OTS + PCM unit I-V module, and V is the voltage applied from the outside received by the OTS + PCM unit I-V module; i is_thFor presetting a current threshold value, V_thIs a preset voltage threshold value, and alpha is a proportionality coefficient;

if the externally applied excitation is a voltage V, V is V_OTS+V_PCM；

If the externally applied excitation is a current I, I ═ I_OTS＝I_PCM。

3. The OTS + PCM cell simulation system for a three-dimensional phase change memory according to claim 1 or 2, wherein the temperature expression of the PCM cell is:

wherein, I_PCMIs the current on the PCM cell, V_PCMIs the voltage across the PCM cell, T is the temperature of the PCM cell, T₀Is the ambient temperature, r_tbIs the lower electrode thermal resistance, r_tgstIs PCM cell thermal resistance, r_ttIs the upper electrode heat resistance, C_tT is the time for the PCM cell heat capacity.

4. The OTS + PCM cell simulation system for a three-dimensional phase change memory of claim 1, wherein the temperature of the PCM cell is compared to the melting point and crystallization temperature of the phase change material of the PCM cell; if the temperature of the PCM unit is higher than the melting point of the phase-change material, the PCM unit is in an amorphous state, and the crystallization rate of the PCM unit is 0 at the moment; if the temperature of the PCM cell is lower than the melting point of the phase change material and higher than the crystallization temperature, the PCM cell is in a crystallized state, and the amorphization rate of the PCM cell is 0.

5. The OTS + PCM cell simulation system for a three-dimensional phase change memory of claim 1, wherein the real-time phase change rate is:

V_a＝V_acF_cF_ac+V_aaF_aa，

wherein, V_acFor crystallization rate, V_aaIn order to obtain the rate of amorphization,

t is the temperature of the PCM cell, T_cFor crystallization temperature, T_aAlpha is the proportionality coefficient for the melting point temperature.

6. The OTS + PCM cell simulation system for a three-dimensional phase change memory according to claim 1, 4 or 5, wherein the crystallization rate is obtained by calculating the sum of the nucleation rate and the growth rate based on nucleation-growth theory according to the PCM cell temperature.

7. The OTS + PCM cell simulation system for three-dimensional phase change memory according to claim 1, 4 or 5, wherein the amorphization rate V_aa＝a(T-T_m)/h₁r_ta(ii) a Where T is the temperature of the PCM cell, T_mMelting point of phase change layer of PCM cell, h₁Is the latent heat of fusion of the PCM cell, r_taA is the thermal resistance of the amorphized region of the PCM cell and a is the proportionality coefficient.

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