CN100543875C - The programmed method of nonvolatile memory - Google Patents
The programmed method of nonvolatile memory Download PDFInfo
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- CN100543875C CN100543875C CNB2004100741611A CN200410074161A CN100543875C CN 100543875 C CN100543875 C CN 100543875C CN B2004100741611 A CNB2004100741611 A CN B2004100741611A CN 200410074161 A CN200410074161 A CN 200410074161A CN 100543875 C CN100543875 C CN 100543875C
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Abstract
The present invention uses fixing reference level, the problem that but has program rate to be difficult to promote when solving programming nonvolatile memory.Therefore the present invention proposes a kind of programmed method of nonvolatile memory, and it does not use fixing reference level and can avoid excessively programming and store the problem that nargin narrows down between attitude.Programmed method is the selected reference level of the accurate distribution scenario in position according to the storage unit of current storage attitude in the nonvolatile memory, according to this reference level predetermined storage unit is programmed to next again and stores attitude.Wherein, the span of reference level is to store between the accurate distribution of lowest order of storage unit of attitude with next between the most significant digit of the storage unit of this current storage attitude is accurate.
Description
Technical field
The present invention relates to is the method for operating of a kind of memory assembly (memory device), and the programmed method of particularly relevant a kind of nonvolatile memory (non-volatile memory).
Background technology
Because programmable nonvolatile memory can be in order to improving the elasticity of circuit design, and still can preserve the advantage of data when having light and handy and non-transformer, so its related application is more and more wide.In the programmed method of known nonvolatile memory, all be to use fixing reference level (reference level) to distinguish the data storing state of storage unit (hereinafter be called for short and store attitude), this reference level may be electric current or start voltage (threshold voltage, V
T) reference level.
(one-timeprogrammable OTP) during nonvolatile memory, is to use a fixing reference level to be known in the one-time programming of the every cell stores of programming 1 (1-bit per cell); And at programming multi-level unit (multi-level cell, MLC) storer or the (multi-timeprogrammable that can repeatedly programme, MTP) during storer, then can use several fixing reference levels, shown in Fig. 1～2, wherein Fig. 1 (A) is presented under the perfect condition, stores the accurate distribution in storage unit position of attitude and the relation between each fixed reference position standard in the MLC storer of every storage unit 2 (2-bit per cell).Fig. 2 (A) then is under the perfect condition, and the MTP storer is after the 1st time and the 2nd time is programmed, and each stores the accurate distribution in storage unit position of attitude and the relation between each fixed reference position standard.
Yet, when programming nonvolatile memory, use fixing reference level, the problem that but has program rate to be difficult to promote.This is that the degree that writes of storage unit is difficult for stable control, and is easy to generate the problem of excessive programming (over-programming), causes accurate distribution the in position of storage unit to broaden because when improving program rate.Shown in Fig. 1 (B) or 2 (B), nargin (inter-state window, code name w) promptly can narrow down between the storage attitude of MLC or MTP storer at this moment, and causes the problem of data value erroneous judgement easily.
Summary of the invention
In view of this, the programmed method for a kind of nonvolatile memory of proposition of the object of the invention, it can be avoided excessively programming and store the problem that nargin narrows down between attitude.
Another object of the present invention is for proposing a kind of programmed method of nonvolatile memory, the problem that is difficult to promote with the speed that solves known programmed method.
Another purpose of the present invention is for proposing the programmed method of a kind of multi-level unit (MLC) nonvolatile memory, and it is to use nonvolatile memory programmed method of the present invention and get.
A further object of the present invention is for proposing a kind of programmed method of (MTP) nonvolatile memory of can repeatedly programming, and it is to use nonvolatile memory programmed method of the present invention and get.
The programmed method of nonvolatile memory of the present invention is the position accurate distribution scenario selected reference level of elder generation according to the storage unit of current storage attitude in the nonvolatile memory, again according to this reference level, predetermined storage unit is programmed to next stores attitude.Wherein, the span of reference level is between the lowest order standard of storage unit of and next storage attitude accurate between the most significant digit of the storage unit of current storage attitude.The position that so-called herein " position is accurate " can be electric current is accurate, also can be that the position of start voltage is accurate, decides according to the kind of nonvolatile memory.
In preferred embodiment of the present invention, when the span of this reference level is accurate when next stores between the lowest order standard of storage unit of attitude with this between the most significant digit of the storage unit of this current storage attitude, the storage unit position standard of next storage attitude is higher than the storage unit position standard of this storage attitude.In addition, above-mentioned nonvolatile memory can be one-time programming (OTP) storer, (MTP) storer of can repeatedly programming, multi-level unit (MLC) storer, but or program resistance need not wipe storer (Programmable Resistor with Erase-less Memory, PREM) or the like.
The programmed method of multi-level unit of the present invention (MLC) nonvolatile memory promptly is a programmed method of using the invention described above, and from the minimum storage attitude starting program of position standard.The MLC nonvolatile memory that can have accurate the 1st to the N storage attitude from low to high in position for each storage unit, the method is that the initial value of order storage attitude pointer i is 1, repeating step (a)-the store accurate selected i reference level that distributes in storage unit position of attitude then according to i, and step (b)-according to the i reference level predetermined storage unit is programmed to i+1 to store attitude, till the programming of N storage attitude is finished, all the i value is added 1 before wherein repeating, and the span of i reference level is to store between the lowest order standard of the accurate storage unit with i+1 storage attitude of the most significant digit of storage unit of attitude between i at every turn.
The programmed method that can repeatedly programme (MTP) nonvolatile memory of the present invention also is the application of the programmed method of the invention described above.At first, according to the accurate selected reference level that distributes in the position of all storage unit, the storage attitude of reseting each storage unit then is the first storage attitude.Then, according to this reference level partial memory cell is programmed for second and stores attitude.Wherein, the span of reference level is to store between the lowest order standard of the accurate storage unit with the second storage attitude of the most significant digit of storage unit of attitude between first.
Because the programmed method of nonvolatile memory of the present invention does not use fixing reference level, but select reference level according to an accurate distribution scenario in storage unit position that stores attitude, reference level is programmed to next with predetermined storage unit and stores attitude according to this again, so reference level can cooperate the actual distribution situation of storage unit position standard to adjust, and can not produce the problem that nargin narrows down between attitude that stores.Therefore, the present invention can solve the problem of data value erroneous judgement.Simultaneously, because reference level can cooperate the actual distribution situation of storage unit position standard to adjust, be the accurate distribution range in storage unit position of tolerable broad so use method of the present invention, that is to say that tolerable uses higher program rate.
For above and other objects of the present invention, feature and advantage can be become apparent, preferred embodiment cited below particularly, and conjunction with figs. elaborate:
Description of drawings
Fig. 1 (A) is under perfect condition, the accurate distribution in position of storage unit and the relation between each fixed reference position standard in the MLC storer that every storage unit is 2;
Fig. 1 (B) is the situation when excessively programming.
Fig. 2 (A) is under perfect condition, and MTP storer is for the first time and after the programming for the second time, wherein the position of storage unit accurate distribute and each fixed reference position standard between relation;
Fig. 2 (B) is the situation when excessively programming.
Fig. 3 is the process flow diagram of method of programming multi-level unit (MLC) nonvolatile memory of preferred embodiment of the present invention.
Fig. 4 is the process flow diagram of programmed method of (MTP) nonvolatile memory of can repeatedly programming of preferred embodiment of the present invention.
Fig. 5 is the method for programming multi-level unit (MLC) nonvolatile memory of preferred embodiment of the present invention, and it is that can to store 2 situation with each storage unit be example.
Fig. 6 is in the preferred embodiment of the present invention, uses the example of the process that method of the present invention repeatedly programmes to the MTP nonvolatile memory.
The figure number explanation
310～350,410～440: step numbers
Embodiment
Hereinafter, though the programmed method of nonvolatile memory of the present invention is that the programmed method with multi-level unit (MLC) nonvolatile memory and (MTP) nonvolatile memory of can repeatedly programming is an example, but according to spirit of the present invention, the present invention be when can be applicable to better simply one-time programming (OTP) nonvolatile memory, and on the more complicated multidigit standard, multiple programmable nonvolatile memory.
Figure 3 shows that the process flow diagram of programmed method of multi-level unit (MLC) nonvolatile memory of preferred embodiment of the present invention.When the programming beginning (step 310), be that a shilling initial value that stores attitude pointer i is 1.Then store the accurate selected i reference level (step 320) that distributes in position of the storage unit of attitude according to i, its value is higher than the most significant digit standard that i stores the storage unit of attitude.Then, according to the i reference level predetermined storage unit is programmed to i+1 and stores attitude (step 330), the lowest order standard that this i+1 stores the storage unit of attitude is higher than the i reference level.Then, judge whether programming has finished (step 340), and whether the programming of the storage attitude of most significant digit standard was just carried out.As unfinished, promptly get back to step 320 and circulate again, till the programming of the storage attitude of most significant digit standard is finished (step 350), all the i value is added 1 before wherein repeating at every turn.
Figure 4 shows that the process flow diagram of programmed method of (MTP) nonvolatile memory of can repeatedly programming of preferred embodiment of the present invention.Begin (step 410) afterwards at programming operation, the accurate distribution in the position of the storage unit of MTP nonvolatile memory selected reference level according to this earlier, its value is the most significant digit standard that is higher than each storage unit, and the storage attitude of reseting each storage unit then is an a certain storage attitude (step 420).Then, according to this reference level partial memory cell is programmed for another and stores attitude (step 430), this programming operation promptly finishes (step 440), and wherein another lowest order standard that stores the storage unit of attitude is to be higher than reference level.
Figure 5 shows that the programmed method of multi-level unit (MLC) nonvolatile memory of preferred embodiment of the present invention, it is can store 2 with each storage unit, is example and have accurate 00,01,10 and the 11 4 kind of situation that stores attitude from low to high in position.As shown in Figure 5, at first determine accurate distribution the in the position of all storage unit when all not programmed, it i.e. the 1st accurate distribution the in storage unit position that stores attitude (00), select then one accurate in 00 position that stores more than the most significant digit standard of attitude as the 1st reference level.Then predetermined storage unit is programmed to the 2nd and stores attitude (01), and make the 01 lowest order standard that stores attitude be higher than the 1st reference level according to the 1st reference level.The decision of follow-up the 2nd reference level and the 3rd stores the programming of attitude (10), and the programming of the decision of the 3rd reference level and the 4th storage attitude (11), can successively carry out according to preceding method.
In addition, select in will definitely the self-editing Cheng Qian default a plurality of candidate's reference levels of above-mentioned each reference bit.Please refer to Fig. 5, this example is earlier default a plurality of candidate's reference level A～K.After the accurate distribution in the storage unit position that determines 00 storage attitude, can be higher than 00 certainly and store among each candidate's reference level A～K of most significant digit standard of storage unit of attitude, select can cooperate candidate's reference level A of nargin between the storage attitude of being scheduled to as the 1st reference level.After the programming of finishing 01 storage attitude according to the 1st reference level, can be higher than 01 certainly and store among each candidate's reference level D～K of most significant digit standard of storage unit of attitude, select can cooperate candidate's reference level D of nargin between the storage attitude of being scheduled to as the 2nd reference level.The rest may be inferred, after the programming of finishing 10 storage attitudes according to the 2nd reference level, can be higher than 10 certainly stores among each candidate's reference level G～K of most significant digit standard of storage unit of attitudes, the candidate's reference level G that selects to cooperate nargin between the storage attitude of being scheduled to is as the 3rd reference level, and then the 3rd reference level carries out the programming operation of last 11 storage attitudes according to this.
Moreover, above-mentioned MLC nonvolatile memory for example is that a programmable resistance need not wiped storer (PREM), its memory cell structure comprises p type semiconductor layer and the n type semiconductor layer of separating with very thin dielectric layer, and be to utilize to apply the electric current position standard that dielectric layer progression collapse phenomenon that voltage causes changes storage unit, programming, and that wherein set reference level is the position of electric current is accurate.The characteristic of PREM is that memory cell current can increase with the voltage or the time of programming, so it is accurate to be programmable to a plurality of different positions, and can be used as the MLC nonvolatile memory.Simultaneously, because progression collapse phenomenon is irreversible process, so when programming is used as the PREM of MLC nonvolatile memory, must be from the minimum storage attitude starting program of position standard.
In addition, though above-mentioned explanation is that can to store 2 situation with each storage unit be example, by principle of the present invention as can be known, the present invention is as limit, and can store 3 or more on the programmable non-volatile memory of multidigit when can be applicable to every storage unit.
In the preferred embodiment of the present invention shown in Figure 6, the process of using method of the present invention that the MTP nonvolatile memory is repeatedly programmed, it is with 1 of each cell stores, and the 1 storage unit position standard that stores attitude to be higher than 0 situation that stores attitude be example.As shown in Figure 6,, at first determine position accurate distribute of all storage unit when not programmed the 1st when programming, selected according to this again reference level, its value is higher than the most significant digit standard of each storage unit.Then, the storage attitude of each storage unit is reset to 0, again according to selected reference level, predetermined storage unit is programmed to 1 stores attitude, its lowest order standard is to be higher than this reference level.Carry out the 2nd time backward if needed and programme, then determine the 1 storage unit position standard that stores attitude earlier and distribute, selected according to this newer reference level, its value is higher than the most significant digit standard of the storage unit of 1 storage attitude.Then, the storage attitude of each storage unit is reset to 0, again according to new selected reference level, predetermined storage unit is programmed to 1 stores attitude, its lowest order standard is to be higher than new selected reference level.As for the 3rd time and subsequent programmed method, when can the rest may be inferred.
Similarly, above-mentioned each reference bit will definitely be selected in a plurality of candidate's reference levels promptly default before the programming for the first time.Please refer to Fig. 6, this example is earlier default a plurality of candidate's reference level A～K.The position that determines all not programmed storage unit is accurate distribute after, can be higher than certainly among each candidate's reference level A～K of most significant digit standard of storage unit, the candidate's reference level A that selects to cooperate nargin between required storage attitude is as with reference to a standard.Afterwards in the 2nd programming, after the 1 accurate distribution in position that stores the storage unit of attitude determines, can be higher than 1 certainly and store among each candidate's reference level D～K of most significant digit standard of storage unit of attitude, the candidate's reference level D that selects to cooperate nargin between required storage attitude is as with reference to a standard.
In addition, above-mentioned (MTP) nonvolatile memory of can repeatedly programming also for example is aforesaid PREM.As previously mentioned, because the memory cell current of PREM can increase with the accumulation of programming time,, as shown in Figure 6, and can be used as the MTP nonvolatile memory so can in usable range, repeatedly improve the electric current position standard of storage unit.Simultaneously, because progression collapse phenomenon is irreversible process,, can not reduce so the electric current position standard of storage unit can only improve when programming each time.
As mentioned above, because the method for programming nonvolatile memory of the present invention is to come motor-driven adjustment reference level according to the accurate distribution scenario of the actual bit of storage unit,, and can solve the problem of data value erroneous judgement so unlikely generation stores the problem of nargin reduction between attitude.Simultaneously, because reference level can cooperate the distribution scenario of storage unit position standard to adjust,, that is to say that tolerable uses higher program rate so, can allow the accurate distribution range in storage unit position of broad as using method of the present invention.
Though the present invention discloses as above with preferred embodiment; yet be not in order to limiting the present invention, anyly have the knack of this operator, without departing from the spirit and scope of the present invention; when can doing various changes and modification, so protection scope of the present invention is when according to being as the criterion of being defined in the claim.
Claims (16)
1. the programmed method of a nonvolatile memory is characterized in that comprising:
According to the accurate distribution scenario in position of the storage unit of current storage attitude in this nonvolatile memory, a selected reference level; And
According to this reference level, predetermined storage unit is programmed to next storage attitude of this storages attitude, wherein
The span of this reference level is between the lowest order standard of the storage unit of the most significant digit standard of the storage unit of this current storage attitude and this next storage attitude.
2. the programmed method of nonvolatile memory as claimed in claim 1, it is characterized in that: when the span of this reference level is accurate when next stores between the lowest order standard of storage unit of attitude with this between the most significant digit of the storage unit of this current storage attitude, the storage unit position standard of next storage attitude is higher than the storage unit position standard of this current storage attitude.
3. the programmed method of nonvolatile memory as claimed in claim 2 is characterized in that: the method for selected this reference level comprises:
Default a plurality of candidate reference levels; And
By selecting one in each the candidate reference level more than the most significant digit standard of the storage unit of this current storage attitude as this reference level.
4. the programmed method of nonvolatile memory as claimed in claim 1 is characterized in that: nonvolatile memory be selected from the one-time programming storer, repeatedly programmable memory, multilevel cell memory and programmable resistance need not wiped storer.
5. the programmed method of nonvolatile memory as claimed in claim 1 is characterized in that: the storage attitude of these storage unit is to decide according to its memory cell current, and this reference level is a current reference position standard.
6. the programmed method of nonvolatile memory as claimed in claim 1 is characterized in that: the storage attitude of these storage unit is to decide according to its storage unit starting voltage, and this reference level is a start voltage reference level.
7. the programmed method of a multi-level unit nonvolatile memory is characterized in that: the storage unit of this multi-level unit nonvolatile memory have the position accurate from low to high the 1st to N store an attitude, and this method comprises:
(a) store accurate distribution the in position of the storage unit of attitude according to i, selected i reference level;
(b), a plurality of storage unit are programmed to i+1 store attitude according to this i reference level; And
In regular turn repeating step (a) with (b), till the programming of N storage attitude is finished, wherein the initial value of i is 1, and all the i value is added 1 before repeating, and the span of i reference level is to store between the lowest order standard of the accurate storage unit with i+1 storage attitude of the most significant digit of storage unit of attitude between i at every turn.
8. the programmed method of multi-level unit nonvolatile memory as claimed in claim 7 is characterized in that also comprising:
Carry out step (a) and (b) presetting a plurality of candidate reference levels before;
And step (a) comprising:
Store by i in each the candidate reference level more than the most significant digit standard of storage unit of attitude and select one as the i reference level.
9. the programmed method of multi-level unit nonvolatile memory as claimed in claim 7 is characterized in that: the storage attitude of these storage unit is to decide according to its start voltage, and these reference levels are the start voltage reference level.
10. the programmed method of multi-level unit nonvolatile memory as claimed in claim 7 is characterized in that: the storage attitude of these storage unit is to decide according to its memory cell current, and these reference levels are current reference position standard.
11. the programmed method of multi-level unit nonvolatile memory as claimed in claim 10 is characterized in that: this multi-level unit nonvolatile memory comprises that programmable resistance need not wipe storer.
12. the programmed method of programming nonvolatile memory repeatedly is characterized in that comprising:
According to this accurate selected reference level that distributes in position of the storage unit of programming nonvolatile memory repeatedly;
The storage attitude of reseting each storage unit is the first storage attitude; And
According to this reference level, predetermined storage unit is programmed for second stores attitude,
Wherein, the span of this reference level stores between the lowest order standard of the accurate storage unit with the second storage attitude of the most significant digit of storage unit of attitude between first.
13. the programmed method of repeatedly programming nonvolatile memory as claimed in claim 12 is characterized in that: the method for selected reference level comprises:
Default a plurality of candidate's reference levels; And
By selecting one in each the candidate's reference level more than the most significant digit standard of these storage unit as accurate with reference to the position.
14. the programmed method of repeatedly programming nonvolatile memory as claimed in claim 12 is characterized in that: the storage attitude of these storage unit is to decide according to its start voltage, and this reference level is a start voltage reference level.
15. the programmed method of repeatedly programming nonvolatile memory as claimed in claim 12 is characterized in that: the storage attitude of those storage unit is to decide according to its memory cell current, and this reference level is a current reference position standard.
16. the programmed method of repeatedly programming nonvolatile memory as claimed in claim 15 is characterized in that: this repeatedly programming nonvolatile memory comprise that programmable resistance need not wipe storer.
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