Method for predicting maximum available erasing times of Flash memory

Abstract

The invention provides a method for predicting the maximum available erasing times of a Flash memory, mainly aims at the Flash memory, emphatically determines the use suggestion of the Flash memory under specified conditions to avoid the reliability hidden danger of the Flash memory caused by excessive erasing, and provides a data retention performance calculation method considering the erasing times. And predicting the maximum available erasing times of the Flash memory under the specified condition. The method comprises the following steps of: 1, determining an allowable Flash memory data retention duration required value at a certain temperature by fitting data retention performance test data; 2, solving a possible value N of erasing times according to a data retention duration required value; 3, calculating a data retention time possible value under an acceleration test condition; 4, calculating a possible value of an acceleration factor; 5, calculating a possible value of data retention time under a non-accelerated test condition; and 6, comparing the relationship between the possible value and the required value. If the possible value is gt; n is a required value, and N is the maximum number of times of erasing under the requirement; if the possible value is lt; if the value is required, N needs to be decreased progressively, and the previous calculation process is repeated until the requirement is met; and step 7, obtaining the maximum available erasing times, and giving a use suggestion of the Flash memory under the requirement. The suggested format is as follows: the Flash memory meets the condition that the maximum available erasing times can be performed at the specified temperature and the set data retention duration is N times.

Description

Technical fields:

[0001] This invention relates to the field of integrated circuit lifetime prediction, and in particular to a method for predicting the maximum number of erase / write cycles of a Flash memory, which belongs to the category of predicting the remaining lifetime of a Flash memory under application conditions. Background technology:

[0002] Flash memory is virtually ubiquitous in electronic devices. However, the floating gate structure design also brings unavoidable problems to the reliability of Flash memory. The most prominent issue is that before writing new data, Flash memory must undergo an erase operation to restore each memory cell to an unprogrammed state, which severely affects the write speed of Flash. In addition, repeated erase and write operations also lead to a decrease in the data retention performance of Flash memory.

[0003] For Flash memory, reliability refers to the accuracy and integrity of the data it stores, mainly encompassing write / erase resistance and data retention performance. During Flash memory operation, the most significant reliability issues arise during write / erase cycles and data retention, in addition to write interference and read interference.

[0004] The main impact of read and write interference on the data held in Flash memory is that a weak electric field appears in the oxide layer when read and write voltages are applied, causing a small number of channel electrons to enter the storage medium, ultimately leading to data errors. Furthermore, floating-gate structure storage layers may also experience coupling crosstalk, resulting in erroneous writes.

[0005] Due to the aforementioned reliability issues, the main reliability metrics for Flash memory are endurance and data retention. Endurance refers to the memory's ability to retain a certain storage window after multiple erase / write cycles; that is, the threshold voltage distribution after writing data cannot be too dispersed. Typically, Flash memory is required to have 100,000 erase / write cycles at room temperature. Data retention refers to the memory's ability to maintain the data read results unchanged after a period of time under certain environmental conditions. It is typically required that data stored at room temperature remain unchanged for 10 years without read errors, and some high-reliability devices require a storage time at 55°C.

[0006] Although there are several existing domestic and international standards for testing the data retention performance of flash memory, such as GJB 548B-2005, MIL-STD-883K, GB / T 35003-2018, AEC-Q100-005, JEP122H-2016, and JESD47K-2018, as shown in Table 1, some standards do not specify the conditions for data retention performance testing, some standards do not consider the number of erase / write cycles, or although erase / write cycles are performed, no calculation method for data retention performance considering the number of erase / write cycles is given.

[0007] In practical applications of Flash memory, erase-write cycles are unavoidable. Therefore, testing the data retention performance of Flash memory using the above standards still carries certain risks. Furthermore, in actual use, it is necessary to clearly define usage recommendations for Flash memory under specific conditions. For example, if the allowable data retention time at a certain temperature is known, it is necessary to determine the maximum number of erase-write cycles the Flash memory can withstand to avoid over-erasing and writing, which could lead to reliability issues. Therefore, it is essential to develop a method for predicting the maximum number of usable erase-write cycles of Flash memory under specified application conditions and to provide usage recommendations.

[0008] This invention primarily targets Flash memory, focusing on providing usage recommendations for Flash memory under specified conditions to avoid reliability risks caused by excessive erasing and writing. It also provides a data retention performance calculation method that takes into account the number of erasing and writing cycles, predicting the maximum usable number of erasing and writing cycles for Flash memory under specified conditions. Summary of the Invention:

[0009] 1. Objective: To address the shortcomings of existing technologies, this invention proposes a method for predicting the maximum number of usable erase / write cycles for Flash memory.

[0010] 2. Technical Solution:

[0011] This invention primarily targets Flash memory, focusing on providing recommendations for the use of Flash memory under specified conditions to avoid reliability risks caused by excessive erasing and writing, and providing a method for calculating data retention performance considering the number of erasure and write cycles.

[0012] This invention proposes a method for predicting the maximum number of usable erase / write cycles of a Flash memory, which includes the following steps:

[0013] Step 1: Determine the allowable data retention time requirement for Flash memory at a specific temperature. By fitting the data retention performance test data, a fitting formula for the mean time to failure (MTBF) and the number of erase / write cycles can be obtained. The data retention time t under any number of erase / write cycles can be calculated as:

[0014] t = exp(AlogN) i +b) (1)

[0015] In the formula, A and b are constants, where A is the slope in the fitted relation and b is the intercept in the fitted relation.

[0016] Step 2: Based on the required data retention time, calculate the possible number of erase / write cycles, N. Under the performance retention test temperature and given a specific data retention time requirement, the maximum number of erase / write cycles, N, can be calculated as follows:

[0017]

[0018] In the formula, t i The duration of Flash memory data retention at the test temperature;

[0019] A is the slope in the fitted relation;

[0020] b is the intercept in the fitted relation.

[0021] To calculate data retention time at other temperatures, an acceleration factor A that accounts for the number of erase / write cycles must first be obtained. TN .

[0022] The impact of erase / write cycles on memory damage is mainly reflected in its effect on activation energy. Considering the activation energy E of erase / write cycles N... AN for:

[0023] E AN =E A0 +C·logN (3)

[0024] In the formula, E A0 The original activation energy before erasure is specified in IEC 60747-10 "General Specification for Semiconductor Discrete Devices and Integrated Circuits", which can be 0.5 eV. N is the number of erase / write cycles, and C is an empirical constant, usually taken as 0.07.

[0025] Assuming the memory data retention failure conforms to the Arrhenius model, the acceleration factor A T for:

[0026]

[0027] In the formula, A T As an acceleration factor;

[0028] t U Data retention time under non-accelerated testing conditions;

[0029] t A To accelerate data retention time under experimental conditions;

[0030] E A To activate energy;

[0031] K is the Boltzmann constant (K = 8.6171 × 10⁻⁶). -5 eV / K);

[0032] T U Temperature under non-accelerated test conditions;

[0033] T A To accelerate the temperature under test conditions.

[0034] By combining equations (3) and (4), an acceleration factor A that takes into account the number of erase / write cycles can be obtained. TN The calculation formula is as follows:

[0035]

[0036] In the formula, the empirical constant C is obtained by fitting actual experimental data, and the calculation formula is:

[0037]

[0038] By combining equations (2) and (4), the maximum number of erase / write cycles that meet the requirements of other temperatures and data retention times can be calculated:

[0039]

[0040] Considering acceleration factor A T Due to the influence of the number of erase / write cycles, substituting equation (5) into equation (7) above yields:

[0041]

[0042] After simplifying equation (8), we get:

[0043]

[0044] In the formula:

[0045] N represents the number of erase / write cycles;

[0046] t U Data retention time under non-accelerated testing conditions;

[0047] T U Temperature under non-accelerated test conditions;

[0048] T A To accelerate the temperature under test conditions;

[0049] E a0 The original activation energy before erasure is set to 0.5 eV.

[0050] K is the Boltzmann constant, with a value of 8.6171 × 10⁻⁶. -5 eV / K;

[0051] A is the slope in the fitted relation;

[0052] b is the intercept in the fitted relation.

[0053] Step 3: Calculate the data retention time t under accelerated testing conditions. A Possible values. Based on the established fitting relationship between average failure time and number of erase / write cycles, we know that:

[0054] t A =exp(AlogN i +b) (10)

[0055] In the formula, A and b are constants, where A is the slope in the fitted relation and b is the intercept in the fitted relation.

[0056] Step 4: Calculate the acceleration factor A T The possible values ​​of the acceleration factor are as follows. According to equation (5), the possible values ​​of the acceleration factor are:

[0057]

[0058] In the formula, the empirical constant C is obtained by fitting actual experimental data.

[0059] Step 5: Calculate the data retention time t under non-accelerated test conditions. U Possible values.

[0060] t U =A T *t A (12)

[0061] Step Six: Compare t U The relationship between possible values ​​and required values.

[0062] If the possible value is greater than the required value, then N is the maximum number of erase / write operations that can be performed under this requirement;

[0063] If the possible value is less than the required value, then N needs to be decremented and the previous calculation process repeated until the requirement is met.

[0064] Step 7: Obtain the maximum number of erase / write cycles and provide recommendations for the use of the flash memory under this requirement.

[0065] The recommended format is: The Flash memory can be erased and written a maximum of N times under a specified temperature and a specified data retention time.

[0066] 3. Advantages and effects:

[0067] This invention proposes an experimental scheme for evaluating the data retention performance of a prototype memory, which has the following advantages:

[0068] (1) In the actual use of Flash memory, erase-write cycles are unavoidable, and the results of testing the data retention performance of Flash memory using existing technology still carry certain risks. This invention calculates the maximum number of erase-write cycles based on the data retention duration, which can further reduce the risks associated with existing technology.

[0069] (2) Provide usage recommendations for Flash memory under specified operating conditions, such as the maximum number of erase / write cycles that Flash memory can perform under specified temperature and specified data retention time is N, which can provide basic data for evaluating the data retention performance of Flash memory; Attached image description:

[0070] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0071] Figure 1 This is a flowchart of a method for predicting the maximum number of erase / write cycles for Flash memory. Implementation method:

[0073] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0074] like Figure 1 As shown, a method for predicting the maximum number of erase / write cycles for a Flash memory includes the following steps:

[0075] Step 1: Determine the allowable data retention time requirement for Flash memory at a specific temperature. By fitting the data retention performance test data, a fitting formula for the mean time to failure (MTBF) and the number of erase / write cycles can be obtained. The data retention time t under any number of erase / write cycles can be calculated as:

[0076] t = exp(AlogN) i +b) (1)

[0077] In the formula, A and b are constants, where A is the slope in the fitted relation and b is the intercept in the fitted relation.

[0078] The Flash memory selected in this embodiment is GD25Q16CSIG, specifically designed for data retention of 30 years (calculated as 260,000 hours) at 55°C. The fitting equation is: lnMTTF i=-0.7736logN+8.9380; A=-0.7736, b=8.9380.

[0079] Step 2: Based on the required data retention time, calculate the possible number of erase / write cycles, N. Under the test temperature and given a specific data retention time requirement, the maximum number of erase / write cycles, N, can be calculated as follows:

[0080]

[0081] In the formula, t i The duration of data retention in the Flash memory at the test temperature is given by A, where A is the slope in the fitted equation and b is the intercept in the fitted equation.

[0082] To calculate data retention time at other temperatures, an acceleration factor A that accounts for the number of erase / write cycles must first be obtained. TN .

[0083] The impact of erase / write cycles on memory damage is mainly reflected in its effect on activation energy. Considering the activation energy E of erase / write cycles N... AN for:

[0084] E AN =E A0 +C·logN (3)

[0085] In the formula, E A0 The original activation energy before erasure is specified in IEC 60747-10 "General Specification for Semiconductor Discrete Devices and Integrated Circuits", which can be 0.5 eV. N is the number of erase / write cycles, and C is an empirical constant, usually taken as 0.07.

[0086] Assuming the memory data retention failure conforms to the Arrhenius model, the acceleration factor A T for:

[0087]

[0088] In the formula, A T As an acceleration factor;

[0089] t U Data retention time under non-accelerated testing conditions;

[0090] t A To accelerate data retention time under experimental conditions;

[0091] E A To activate energy;

[0092] K is the Boltzmann constant (K = 8.6171 × 10⁻⁶). -5 eV / K);

[0093] TU Temperature under non-accelerated test conditions;

[0094] T A To accelerate the temperature under test conditions.

[0095] By combining equations (3) and (4), an acceleration factor A that takes into account the number of erase / write cycles can be obtained. TN The calculation formula is as follows:

[0096]

[0097] In the formula, the empirical constant C is obtained by fitting actual experimental data, and the calculation formula is:

[0098]

[0099] By combining equations (2) and (4), the maximum number of erase / write cycles that meet the requirements of other temperatures and data retention times can be calculated:

[0100]

[0101] Considering acceleration factor A T Due to the influence of the number of erase / write cycles, substituting equation (5) into equation (7) above yields:

[0102]

[0103] After simplifying equation (8), we get:

[0104]

[0105] In the formula:

[0106] N represents the number of erase / write cycles;

[0107] t U Data retention time under non-accelerated testing conditions;

[0108] T U Temperature under non-accelerated test conditions;

[0109] T A To accelerate the temperature under test conditions;

[0110] E a0 The original activation energy before erasure is set to 0.5 eV.

[0111] K is the Boltzmann constant, with a value of 8.6171 × 10⁻⁶. -5 eV / K;

[0112] A is the slope in the fitted relation;

[0113] b is the intercept in the fitted relation.

[0114] In this embodiment, the selected Flash memory is GD25Q16CSIG. Specifically, The value is close to the commonly used value of 0.07 in engineering. The calculated number of possible erase / write cycles is N = 68.342, which is rounded down to 68.

[0115] Step 3: Calculate the data retention time t under accelerated testing conditions. A Possible values. Based on the established fitting relationship between average failure time and number of erase / write cycles, we know that:

[0116] t A =exp(AlogN i +b) (10)

[0117] In the formula, A and b are constants, where A is the slope in the fitted relation and b is the intercept in the fitted relation.

[0118] In this embodiment, the selected Flash memory is GD25Q16CSIG. Specifically, the data retention time at 150°C is calculated to be t. A = 1844.567 hours, rounded down to 1844 hours.

[0119] Step 4: Calculate the acceleration factor A T The possible values ​​of the acceleration factor are as follows. According to equation (5), the possible values ​​of the acceleration factor are:

[0120]

[0121] In the formula, the empirical constant C is obtained by fitting actual experimental data.

[0122] In this embodiment, the selected Flash memory is GD25Q16CSIG. Specifically, the acceleration factor A after 68 erase / write cycles is calculated. T =140.788, rounded down to 140.

[0123] Step 5: Calculate the data retention time t under non-accelerated test conditions. U Possible values.

[0124] t U =A T *t A (12)

[0125] In this embodiment, the selected Flash memory is GD25Q16CSIG. Specifically, the data retention time t at 55°C is calculated. U =A T ·t A =140*1844=258160.

[0126] Step Six: Compare t U The relationship between possible values ​​and required values.

[0127] If the possible value is greater than the required value, then N is the maximum number of erase / write operations that can be performed under this requirement;

[0128] If the possible value is less than the required value, then N needs to be decremented and the previous calculation process repeated until the requirement is met.

[0129] In this embodiment, the selected Flash memory is GD25Q16CSIG. Specifically, since 258160 < 260000, the possible number of erase / write cycles N is successively decreased by 1 to find the maximum number of erase / write cycles that can be performed. Finally, it is found that when N = 63 cycles, the expected data retention time t at 55°C is... U =260300>260000 hours.

[0130] Step 7: Obtain the maximum number of erase / write cycles and provide recommendations for the use of the flash memory under this requirement.

[0131] The recommended format is: The flash memory can be erased and written a maximum of N times under specified temperature and specified data retention time.

[0132] The Flash memory GD25Q16CSIG selected in this embodiment has a maximum write / erase cycle of 63 times to meet the requirement of data retention for 30 years at 55°C.

Claims

1. A method for predicting the maximum available erasing and writing times of a Flash memory, comprising the following steps: Step S1: Determine the required value of the Flash memory data retention time allowed at a certain temperature; Step S2: By fitting the data retention performance test data, the fitting relationship between the mean failure time and the number of erase and write times can be obtained, and the data retention time t under any number of erase and write times can be calculated, and then the possible value N of the number of erase and write times can be calculated. The data retention time t under any number of erase and write times can be calculated as: t=exp(AlogN i +b) Under a certain data retention time requirement, the maximum number of erase and write times N can be calculated as: Step S3: Based on the activation energy E AN Get the acceleration factor A considering the number of erase and write times TN , considering the activation energy E of the erase and write times N AN for: IN AN =E A0 +C·logN In the formula, E A0 It is the original activation energy before erasure. According to IEC 60747-10 “General Specification for Discrete Semiconductor Devices and Integrated Circuits”, the value can be 0.5eV. N is the number of erases and writes. C is an empirical constant usually taking a value of 0.

07. Assuming that the data retention failure of the memory complies with the Arrhenius model, the acceleration factor A T for: In the formula, A T is the acceleration factor; t U It is the data retention time under non-accelerated test conditions; t A It is the data retention time under accelerated test conditions; E A is the activation energy; K is the Boltzmann constant (K = 8.6171 × 10 -5 eV / K); T U is the temperature under non-accelerated test conditions; T A is the temperature under accelerated test conditions. Combining the above formula, we can get the acceleration factor A considering the number of erase and write times. TN The calculation formula is as follows: In the formula, the empirical constant C is obtained by fitting the actual test data, and the calculation formula is: Step S4: Calculate the data retention time t under the accelerated test condition A Possible values, according to the established fitting relationship between the mean failure time and the number of erase and write times, we can know: t A =exp(AlogN i +b) In the formula, A and b are constants, A is the slope in the fitting equation; b is the intercept in the fitting equation. Step S5: Calculate the data retention time t under non-accelerated test conditions U possible values ​​of t U The relationship between the possible value and the required value. If the possible value > the required value, then N is the maximum number of erase and write times that can be performed under this requirement. If the possible value < the required value, then N needs to be decreased and the previous calculation process is repeated until the requirement is met. U The calculation formula is: t U =A T *t A Step S6: Get the maximum available erase and write times, and give a usage suggestion for the memory under this requirement. The suggestion format is: the maximum available erase and write times that the Flash memory can perform under the specified temperature and the specified data retention time is N times.

Images