CN102564584B - Modeling method for equivalent circuit of high-sensitivity quantum effect photodetector - Google Patents

Abstract

The invention discloses a modeling method for the equivalent circuit of a high-sensitivity quantum effect photodetector. The "VerilogA" language establishes an equivalent circuit model, and then uses circuit simulation software to verify it, providing a photodetector model that accurately reflects the characteristics of different structural devices for the design of the readout circuit. Compared with the prior art, the present invention has the advantages of simple modeling program, flexible modification and high efficiency. The specific data can be directly input in the corresponding pre-set optical power and device bias parameters in the circuit model properties.

Description

Modeling Method of Equivalent Circuit of High Sensitivity Quantum Effect Photodetector

technical field

The invention relates to the technical field of electronics and circuit design, in particular to a modeling method for an equivalent circuit of a high-sensitivity quantum effect photodetector.

Background technique

Photodetectors play the role of converting received light signals into electrical signals. In recent years, with the development of quantum well, quantum dot physics and material technology, quantum effect photodetectors have emerged as the times require. Quantum-effect photodetectors have the advantages of small dark current, high sensitivity, large dynamic range, and high photoelectric conversion efficiency under low-light irradiation. They are widely used in medical, biomolecular science, and environmental monitoring. The main function of the readout circuit in the photodetection system is to preprocess the weak signal of the detector and provide an interface between the signal processing stages. In the design of the readout circuit, a photodetector that can accurately reflect the quantum effect is required. the equivalent circuit.

At present, some equivalent circuit models have been established for some typical photodetector devices, and most of these models are obtained based on the internal physical equations of photodetectors. Due to the excessive number of physical characteristic parameters inside the photodetector device and the approximate expressions obtained based on various assumptions when solving a large number of physical characteristic equations, the accuracy of the equivalent circuit model will be greatly affected. The design of the circuit poses difficulties. Moreover, during the solution process, due to the complex structure of the photodetector and various material parameters used, it will also complicate the programming in the modeling process.

In the patent number: ZL 200910047116.X "A Design Method for Photodetector Readout Circuit", a simple and practical equivalent circuit modeling method is proposed, which is based on the I-V and C-V electrical characteristics of the device. It is concluded that the limitation of this modeling method is that it cannot reflect the I-V and C-V characteristics of photodetectors under different irradiated light powers, and the I-V and C-V characteristics of photodetectors will change with the irradiated light power. Therefore, the current modeling method of the equivalent circuit of the photodetector has certain limitations.

Contents of the invention

The purpose of the present invention is to provide an equivalent circuit modeling method for a high-sensitivity quantum effect photodetector aimed at the deficiencies of the prior art, using the "VerilogA" language to accurately realize photoelectric detection under different irradiation powers and device bias voltages The characteristic parameters of the photodetector are used to establish an equivalent circuit that can be accurately matched with the photodetector. The modeling program is simple and efficient, which greatly reduces the influence of too many physical characteristic parameters inside the photodetector and the establishment of complex programs. , it is very convenient to set, modify and input corresponding to different optical power and device bias parameters, and provide accurate photodetector models that reflect the structural characteristics of different devices for readout circuit design.

The object of the present invention is achieved like this: a kind of modeling method of quantum effect photodetector equivalent circuit of high sensitivity, it is characterized in that quantum dot-quantum well photodetector adopts different radiation power and device bias For the electrical characteristic test, the equivalent circuit model is established by using the "VerilogA" language, and then verified by circuit simulation software to provide a photodetector model that accurately reflects the characteristics of different structural devices for the design of the readout circuit. The specific modeling method includes the following steps:

(1) Testing and fitting of characteristic parameters of photodetectors

，由此在等效电路中可以用一个受控电流源来实现，使输出电流为电压的函数；  a. Based on the photoelectric test platform, make the current-voltage characteristic (I-V) characteristic curve cluster of the photodetector, and use the "Origin" software to obtain the function between I and V under different irradiated light powers by segmental fitting relation:

, so it can be realized with a controlled current source in the equivalent circuit, so that the output current is a function of the voltage;

，并采用“VerilogA”语言对等效电容进行描述，由此在等效电路中可以用一个“VerilogA”语言描述电流源形式的可变电容来实现，其电容大小为电压的函数； b. Based on the photoelectric test platform, make the capacitance-voltage (C-V) characteristic curve cluster of the photodetector, and use the "Origin" software to obtain the functional relationship between C and V under different irradiated light powers by segment fitting :

, and use the "VerilogA" language to describe the equivalent capacitance, so in the equivalent circuit, a "VerilogA" language can be used to describe the variable capacitance in the form of a current source, and its capacitance is a function of voltage;

(2) "VerilogA" language description for the resistance in the equivalent circuit

值为等效电路模型的输出电压，由此得到等效电路模型的输出阻抗

，采用“VerilogA”语言对等效输出电阻进行描述，由此在等效电路中可以用一个“VerilogA”语言描述的电流源形式的输出阻抗来实现；  The reference voltage of the sensing structure in the capacitive feedback transimpedance amplifier (CTIA) type

The value is the output voltage of the equivalent circuit model, and thus the output impedance of the equivalent circuit model is obtained

, using the "VerilogA" language to describe the equivalent output resistance, so that the equivalent circuit can be realized with an output impedance in the form of a current source described in the "VerilogA"language;

(3) Modeling of equivalent circuit

The above-mentioned variable capacitance in the form of a current source described in the "VerilogA" language is connected in parallel with the output impedance in the form of a current source to form an equivalent circuit model that can accurately match the photodetector. the

(4) Simulation of equivalent circuit model

Use the "Spectre" simulator of the circuit simulation software "Cadence" to simulate the equivalent circuit model established above, and compare the simulation results with the actually tested I-V and C-V characteristic curve clusters. Verify the correctness of the equivalent circuit model and provide an accurate photodetector model for the design of the readout circuit. the

Compared with the prior art, the present invention has the following advantages:

1. The circuit modeling program is simple and efficient, which greatly reduces the influence of too many physical characteristic parameters inside the photodetector and the establishment of complex programs that affect the model accuracy;

2. The equivalent circuit can be directly connected to the readout circuit, which is convenient for the photodetector to design a matching readout circuit;

3. Using "VerilogA" language modeling, it is very convenient to set and modify the parameters corresponding to different optical power and device bias voltage. The realization of different optical power and device bias voltage can be achieved through the corresponding preset in the equivalent circuit model properties The specific data can be directly input in the optical power and device bias parameters, and the modification is flexible.

Description of drawings

Figure 1 is a cluster diagram of the low-light I-V characteristic curve of the photodetector;

Figure 2 is a cluster diagram of the low-light C-V characteristic curve of the photodetector;

Figure 3 is a page diagram of the "VerilogA" unit file;

Figure 4 is a schematic diagram of resistance in the form of a current source;

Figure 5 is a diagram of the resistance property page in the form of a current source;

Figure 6 is a schematic diagram of the variable capacitor in the equivalent circuit;

Figure 7 is a simplified photodetector equivalent circuit diagram;

Figure 8 is the I-V characteristic simulation waveform diagram of the equivalent circuit model;

Figure 9 is a simulation waveform diagram of the C-V characteristics of the equivalent circuit model. `` ``

Detailed ways

Below with a kind of embodiment that the quantum effect photodetector with a kind of sensitivity is higher under the light power irradiation below 5nW equivalent circuit modeling, the present invention will be further described, and its specific modeling steps are as follows:

(1) Test of characteristic parameters of photodetectors

Based on the photoelectric test platform, using the Kelthley 4200-SCS semiconductor characteristic analyzer and the He-Ne laser with a wavelength of 633nm, the quantum dot-quantum well photodetectors are tested under the conditions of no light (dark current) and irradiated light power of 0.2 nW and 0.5 nW, 1 nW, 2 nW and 5 nW I-V and C-V electrical characteristic parameters, and make a photodetector electrical characteristic curve cluster.

Referring to accompanying drawing 1, it can be seen that the quantum effect photodetector of this low-light test system has very low noise (pA) at low temperature (120K), and has high sensitivity and low-light characteristics.

Referring to Figure 2, it can be seen that the capacitance of the photodetector changes little under reverse bias.

(2) Fitting of photodetector characteristic curve

和

，其中：V代表器件偏压，P代表辐照光功率，特性曲线的拟合具体步骤如下：  According to the test, the IV and CV characteristic curve clusters of the photodetector are made. In order to realize the high sensitivity of the photodetector, the actual device should work under the reverse bias condition, and use the "Origin" software to fit different irradiated optical powers. The following functional relationship between IV and CV:

and

, where: V represents the bias voltage of the device, P represents the irradiated optical power, and the specific steps of fitting the characteristic curve are as follows:

a. I-V characteristic curve cluster fitting

，由此可以在等效电路中可以用一个受控电流源来实现，使输出电流为电压的函数，I-V特性曲线簇拟合时将器件偏压-3V至0之间分为两段，分别是[-1.5,0]和[-3，-1.5]。 In order to make the fitted characteristic curve coincide well with the IV characteristic curve obtained from the test, the "Origin" software is used to fit the function in sections to obtain the functional relationship between I and V under different irradiated light powers:

, so it can be realized with a controlled current source in the equivalent circuit, so that the output current is a function of the voltage, and the device bias voltage between -3V and 0 is divided into two sections when the IV characteristic curve cluster is fitted, respectively is [-1.5,0] and [-3,-1.5].

函数关系如下式（1）表示：

 （1） When the device bias When the photodetector has no light (dark current) and irradiated light power is 0.2 nW, 0.5 nW, 1 nW, 2 nW and 5 nW respectively

The functional relationship is represented by the following formula (1):

(1)

时，光电探测器在无光照（暗电流）和辐照光功率分别是0.2 nW、0.5 nW 、1 nW、2 nW和5 nW的

函数关系如下式（2）表示：

   （2） When the device bias

When the photodetector has no light (dark current) and irradiated light power is 0.2 nW, 0.5 nW, 1 nW, 2 nW and 5 nW respectively

The functional relationship is represented by the following formula (2):

(2)

b. C-V characteristic curve cluster fitting

，并用“VerilogA”语言对等效电容进行描述，由此可以在等效电路中可以用一个“VerilogA”语言描述电流源形式的可变电容来实现，其电容大小为电压的函数，C-V特性曲线簇拟合在器件偏压[-3,0]范围内采用一次拟合。 In order to make the fitted characteristic curve coincide well with the CV characteristic curve obtained from the test, the "Origin" software is used to fit the function in sections to obtain the functional relationship between C and V under different irradiated light powers:

, and use the "VerilogA" language to describe the equivalent capacitance, so that in the equivalent circuit, a "VerilogA" language can be used to describe the variable capacitance in the form of a current source. The capacitance is a function of voltage, and the CV characteristic curve The cluster fit uses a single fit over the device bias range [-3,0].

时，光电探测器在无光照（暗电流）和辐照光功率分别是0.2 nW、0.5 nW 、1 nW、2 nW和5 nW的函数关系如下式（3）表示：

  （3） When the device bias

When the photodetector has no light (dark current) and irradiated light power is 0.2 nW, 0.5 nW, 1 nW, 2 nW and 5 nW respectively The functional relationship is expressed in the following formula (3):

(3)

(3) "VerilogA" language description for the resistance in the equivalent circuit

，光电探测器的等效电阻如下式（4）表示： The current source implementation of the photodetector equivalent circuit is the functional relationship between IV:

, the equivalent resistance of the photodetector is expressed by the following formula (4):

                     （4）

(4)

值，而输出电流为

，由此可以得到等效电路模型的输出阻抗如下式（5）表示： Since the readout of the photodetector adopts the capacitive feedback transimpedance amplifier (CTIA) structure, the output voltage of the equivalent circuit model of the photodetector is the reference voltage of the CTIA readout circuit

value, while the output current is

, so the output impedance of the equivalent circuit model can be obtained as follows:

          （5）

(5)

值为等效电路模型的输出电压，由此得到等效电路模型的输出阻抗

，并采用“VerilogA”语言对等效输出电阻进行描述，由此在等效电路中可以用一个“VerilogA”语言描述的电流源形式的输出阻抗来实现。  Reference voltage in CTIA-type readout structure

The value is the output voltage of the equivalent circuit model, and thus the output impedance of the equivalent circuit model is obtained

, and use the "VerilogA" language to describe the equivalent output resistance, so the equivalent circuit can be realized by using a "VerilogA" language to describe the output impedance in the form of a current source.

Refer to Figure 3, create a current source form equivalent output resistance "VerilogA" file and "symbol" symbol, create a new "VerilogA" unit file "Cell" under the "Cadence" software, and make a current source form Equivalent output resistance symbol.

Referring to Figure 4, set the device bias voltage and irradiated optical power as the two parameters of "biasvoltage" and "photopower" respectively, and set them in the properties of the equivalent output resistance in the form of a current source. Because the current of the photodetector is affected by the bias voltage of the device and the irradiated light power, and the equivalent output resistance is related to the output current, the resistance in the form of a current source in the equivalent circuit model of the photodetector should have a controlled current source The characteristics are controlled by device bias voltage and irradiated light power.

函数关系进行了描述，所以只要在电流源的属性中将器件偏压和光功率对应的参数“biasvoltage”和“photopower”直接输入数据即可，参数设置和修改都非常方便。 Referring to accompanying drawing 5, since in the above steps, the photodetector has been subjected to light powers of 0.2 nW, 0.5 nW, 1 nW, 2 nW and 5 nW in the absence of light (dark current) and irradiated light power respectively

The functional relationship is described, so as long as the parameters "biasvoltage" and "photopower" corresponding to the device bias voltage and optical power are directly input in the properties of the current source, the parameter setting and modification are very convenient.

For example, when the bias voltage of the device is -2V and the optical power is 1nW, just enter "-2" in the "biasvoltage" option and "1" in the "photopower" option, and use the current source formula described in the "VerilogA" language The equivalent resistance expression of the following formula (6):

(6)

=2.5V，所以电流源式的等效电阻

，在电流源形式的等效输出电阻的“VerilogA”语言描述时定义电流源的两个端口为“ns”和“ps”，并设定器件的偏压和光功率两个参数“biasvoltage”和“photopower”的初值，实际使用时可在器件属性中进行修改，因为I-V特性是分段拟合的，不同的光功率对应不同的I-V曲线，所以在用“VeriolgA” 语言描述时分别使用了“if-else”和“case”语句来实现。    Since the reference voltage of the CTIA-type readout circuit

=2.5V, so the equivalent resistance of the current source

, in the "VerilogA" language description of the equivalent output resistance in the form of a current source, define the two ports of the current source as "ns" and "ps", and set the two parameters of the bias voltage and optical power of the device "biasvoltage" and " The initial value of "photopower" can be modified in the device properties in actual use, because the IV characteristics are fitted in pieces, and different optical powers correspond to different IV curves, so the "VeriolgA" language is used to describe "if-else" and "case" statements.

(4) "VerilogA" language description for the variable capacitance in the equivalent circuit

Refer to Figure 6, create a variable capacitance "VerilogA" file and "Symbol" symbol, create a variable capacitance unit "cell" and "Symbol" symbol, because the capacitance of the photodetector is affected by the device bias and radiation Therefore, the capacitance in the equivalent circuit model of the photodetector should be a variable capacitance controlled by the bias voltage of the device and the irradiated light power. Set the bias voltage of the device and the irradiated optical power as two parameters of "biasvoltage" and "photopower" respectively, the setting and modification methods are the same as the equivalent output resistance of the current source form, and the current source form can be described by "VerilogA" language The expression of the variable capacitance is expressed in the following formula (7):

                   （7）

(7)

，这里的电容C本身也是随器件偏压和光功率变化的，所以电容C必须放在括号里面, 电容 C和器件偏压和光功率的关系为：

。在电流源形式的可变电容“VerilogA”语言描述时，定义了电流源的两个端口为“ns”和“ps”，并设定器件的偏压和光功率两个参数“biasvoltage”和“photopower”的初值，实际使用时可在器件属性中进行修改，因为在器件偏压

范围内的C-V特性曲线是一次拟合的，不同的光功率对应不同的C-V特性曲线，所以在用“VeriolgA” 语言描述时使用了“case”语句来实现。   Right now

, the capacitor C itself also changes with the device bias voltage and optical power, so the capacitor C must be placed in brackets. The relationship between the capacitor C and the device bias voltage and optical power is:

. When describing the variable capacitor in the form of current source "VerilogA", the two ports of the current source are defined as "ns" and "ps", and the two parameters "biasvoltage" and "photopower" of the bias voltage and optical power of the device are set. "The initial value can be modified in the device properties in actual use, because the device bias

The CV characteristic curve within the range is one-time fitting, and different optical powers correspond to different CV characteristic curves, so the "case" statement is used to realize it when described in the "VeriolgA" language.

(5) Modeling of equivalent circuit

Referring to accompanying drawing 7, use "VerilogA" language to describe the controlled current source and equivalent output resistance with a program, and generate a "Symbol" symbol, so that the obtained equivalent circuit model only includes two parts, one part is the current source The other part is a variable capacitor, that is, the photodetector can be equivalent to a circuit model in which a resistor in the form of a current source is connected in parallel with a variable capacitor.

(6) Carry out simulation simulation verification on the equivalent circuit model

Referring to accompanying drawing 8, use the "Spectre" simulator of the circuit simulation software "Cadence" to carry out the equivalent circuit model of the photodetector built above in the device bias voltage [-3,0] respectively. DC analysis and parameter sweep of device bias voltage "biasvoltage" and optical power "photopower" are used to simulate the equivalent circuit model established above. Curve clusters were compared for verification.

Referring to Figure 9, the equivalent circuit model of the above-built photodetector is used for AC analysis of the equivalent circuit model within the device bias voltage [-3,0] and the device bias voltage "biasvoltage" and optical power "photopower "Two parameters are scanned, and the C-V characteristic results of the equivalent circuit model obtained by simulation are compared with the actual test C-V characteristic curve clusters for verification.

By comparing the I-V and C-V simulation curves of the above equivalent circuit model with the actual test I-V and C-V curve clusters, it can be seen that the two can be well matched, verifying that the simulation curves coincide with the actual test I-V and C-V curve clusters , so that the correctness of the equivalent circuit model can be verified, and a photodetector model that accurately reflects the characteristics of different structural devices can be provided for the design of the readout circuit.

The above embodiments are only to further illustrate the present invention, and are not intended to limit the patent of the present invention. All equivalent implementations of the present invention should be included in the scope of claims of the patent of the present invention.

Claims (1)

1. the modeling method of a high sensitivity quantum effect photodetector equivalent electrical circuit, it is characterized in that the quantum-dot-quantum-well photodetector is adopted different irradiation powers and the test of the electrical characteristics under the device bias, use " VerilogA " language and set up equivalent-circuit model, then utilize circuit simulation software to verify, for the design of sensing circuit provides the photodetector that reflects accurately different components architectural characteristic model, concrete grammar comprises the following steps:

(1), the test of the characterisitic parameter of photodetector and match

A, based on the photoelectricity test platform, make I-E characteristic (I-V) characteristic family of photodetector, and adopt piecewise fitting to obtain I under the different exposure light power and the funtcional relationship between the V with " Origin " software:

, can realize with a controlled current source in equivalent electrical circuit that thus making output current is the function of voltage;

B, based on the photoelectricity test platform, make capacitance-voltage (C-V) characteristic family of photodetector, adopt piecewise fitting to obtain C under the different exposure light power and the funtcional relationship between the V with " Origin " software:

, and adopt " VerilogA " language that equivalent capacity is described, in equivalent electrical circuit, can realize that its capacitance size is the function of voltage with the variable capacitance of " VerilogA " language description current source form thus;

(2), the resistance in the equivalent electrical circuit is carried out " VerilogA " language description

Reference voltage with capacitive feedback transreactance amplifier (CTIA) type reading out structure

Value is the output voltage of equivalent-circuit model, obtains thus the output impedance of equivalent-circuit model

, and adopt " VerilogA " language that equivalent output resistance is described, in equivalent electrical circuit, can realize with the output impedance of the current source form of " VerilogA " language description thus;

(3), the modeling of equivalent electrical circuit

The variable capacitance of the current source form of above-mentioned employing " VerilogA " language description is in parallel with the output impedance of current source form, formation can with the accurate equivalent-circuit model of coupling of photodetector;

(4), the analogue simulation of equivalent-circuit model

Equivalent-circuit model with above-mentioned foundation, utilize " Spectre " emulator of circuit simulation software " Cadence " that equivalent-circuit model is carried out analogue simulation, simulation result and I-V and the C-V characteristic family of actual test are compared, verify the correctness of equivalent-circuit model with this, for the design of sensing circuit provides accurately photodetector model.

Images