Fuse circuit

A fuse circuit includes a plurality of fuses, a plurality of switches and a plurality of trimming components. The fuses are coupled in parallel to a first node and a second node. The first node is coupled to an operating voltage. The switches are coupled to the second node. The trimming components are respectively disposed between the switches and a ground voltage, and coupled to the second node via the switches, respectively. When one of the trimming components is activated, the activated trimming component allows a plurality of branch currents to be generated between the first node and the second node. The branch currents respectively flow through the fuses so that one of the fuses is blown out by the branch current flowing through the one of the fuses.

RELATED APPLICATIONS

This application claims priority to Taiwanese Application Serial Number 102138693, filed Oct. 25, 2013, which is herein incorporated by reference.

BACKGROUND

1. Field of Invention

The present invention relates to a fuse circuit. More particularly, the present invention relates to a fuse circuit having a multi-state resistance value.

2. Description of Related Art

In recent years, the fuse circuit has been widely used in memory devices to serve as a one time programming (OTP) memory unit. When the current flowing through the fuse has a current value greater than the critical value, the fuse blows and the resistance value of the fuse is increased. Therefore, the original resistance value of the fuse and the increased resistance value of the fuse respectively represent two logic states, for example, the low resistance state and the high resistance state respectively represent a logic 0 state and a logic 1 state.

However, when the traditional fuse circuit is programmed, the fuse cannot be re-written once it is written (is blown out). Hence, multiple time programming cannot be performed and a multi-state resistance value is not obtained.

SUMMARY

In accordance with an embodiment, the fuse circuit includes a plurality of fuses, a plurality of switches, and a plurality of trimming components. The plurality of fuses are coupled in parallel to a first node and a second node. The first node is coupled to an operating voltage. The plurality of switches are coupled to the second node. The plurality of trimming components are respectively disposed between the switches and a ground voltage, and are coupled to the second node via the switches respectively. When one of the trimming components is activated, the activated trimming component allows a plurality of branch currents to be generated between the first node and the second node. The branch currents respectively flow through the fuses so that one of the fuses is blown out by the branch current flowing through the one of the fuses.

In accordance with another embodiment, the fuse circuit includes a plurality of fuses, a plurality of switches, a plurality of trimming components, a control circuit and a switch control circuit. The plurality of fuses are coupled in parallel to a first node and a second node. The first node is coupled to an operating voltage. The plurality of switches are coupled to the second node. The plurality of trimming components are respectively disposed between the switches and a ground voltage and coupled to the second node via the switches respectively. The control circuit is configured for generating a first control signal and a second control signal to trigger the trimming components. The switch control circuit is configured for selectively controlling the switches. When one of the trimming components is activated, the activated trimming component allows a plurality of branch currents to be generated between the first node and the second node. The branch currents respectively flow through the fuses so that one of the fuses is blown out by the branch current flowing through the one of the fuses.

In accordance with still another embodiment, the fuse circuit includes a plurality of fuses, a low-voltage triggering silicon control rectifier and a control circuit. The plurality of fuses are coupled in parallel to a first node and a second node. The first node is coupled to an operating voltage. The low-voltage triggering silicon control rectifier is coupled to the second node. The control circuit is configured for generating a first control signal and a second control signal to trigger the low-voltage triggering silicon control rectifier. When the low-voltage triggering silicon control rectifier is activated, the low-voltage triggering silicon control rectifier allows a plurality of branch currents to be generated between the first node and the second node. The branch currents respectively flow through the fuses so that one of the fuses is blown out by the branch current flowing through the one of the fuses.

DESCRIPTION OF THE EMBODIMENTS

Various embodiments are described below to explain this invention. However, these embodiments are not intended to limit the application or methods of the present invention in any specific context. Therefore, descriptions of the embodiments are only intended to illustrate rather than to limit the present invention. It should be noted that, in the following embodiments and attached drawings, elements not directly related to this invention are omitted from depiction, and the dimensional relationships depicted among various elements are only for purposes of illustration, rather than limiting the practical implementation of these elements.

As used herein, “couple” refers to direct physical contact or electrical contact or indirect physical contact or electrical contact between two or more components. Or it can also refer to reciprocal operations or actions between two or more components.

FIG. 1Adepicts a schematic diagram of a fuse circuit100according to one embodiment of this invention. The fuse circuit100includes a plurality of fuses F-1˜F-N (N is an integer greater than one), a plurality of switches S-1˜S-P (P is an integer greater than one), and a plurality of trimming components101-1˜101-P. It is noted that the number of the switches S-1˜S-P corresponds to the number of the trimming components101-1˜101-P. In other words, the number of the switches S-1˜S-P is the same as the number of the trimming components101-1˜101-P.

In the present embodiment, the fuses F-1˜F-N may be one time programmable fuses, and the fuses F-1˜F-N may have different resistance values.

In another embodiment, at least two of the fuses F-1˜F-N have different resistance values. For example, the resistance value of the fuse F-1is different from the resistance value of the fuses F-2˜F-N, and the fuses F-2˜F-N have the same resistance value. In another example, the resistance value of the fuse F-1is different from the resistance value of the fuse F-2, the other fuses F-3˜F-N have the same resistance value, and the resistance value of the fuse F-3is different from the resistance value of the fuse F-1and the resistance value of the fuse F-2.

In still another embodiment, each of the fuses F-1˜F-N may include polysilicon, metal, or a metal via. Each of the fuses F-1˜F-N may also be made of another material that may be used for fabricating the fuses F-1˜F-N or in another structure. The resistance value R of a fuse can be obtained by calculating resistivity ρ1, length L, and cross sectional area A. The formula for calculating resistance value R is as follows:
R=ρ1*L/A

When the cross sectional area A and the length L are not changed, the resistance value R only correlates with the resistivity. Under the circumstances, the resistance values of the fuses fabricated from different materials are very different. In one embodiment, the multiple relationships between the resistance values of the fuses fabricated from different materials may range from 10 times to 1000 times.

In yet another embodiment, the multiple relationships between the resistance values of the fuses F-1˜F-N may range from 10 times to 1000 times. For example, the resistance value of the fuse F-1may be 0.1 ohm, the resistance value of the fuse F-2may be 10 ohms, and the resistance value of fuse F-1and the resistance value of the fuse F-2are different from the resistance values of the other fuses F-3˜F-N.

In another embodiment, the multiple relationship between the resistance values of two of the fuses F-1˜F-N may range from 10 times to 1000 times. For example, the resistance value of the fuse F-1may be 10 ohms, and the fuses F-2˜F-N have the same resistance value of 100 ohms. In another example, the resistance values of the fuse F-1and the fuse F-2are respectively 1 ohm and 100 ohms (which are different from each other), and the other fuses F-3˜F-N have the same resistance value of 1000 ohms. It is noted that the above resistance values are only for explanation of aspects of the present embodiment and are not intended to limit the present invention.

In the present embodiment, the fuses F-1˜F-N are coupled in parallel to a first node N1and a second node N2. The first node N1is coupled to an operating voltage VDD. In addition, the switches S-1˜S-P are coupled to the second node N2. The trimming components101-1˜101-P are respectively disposed between the switches S-1˜S-P and a ground voltage GND. Also, the trimming components101-1˜101-P are respectively coupled to the second node N2via the switches S-1˜S-P, respectively.

With respect to the operations, when one of the trimming components101-1˜101-P is activated, the activated trimming component allows a plurality of branch currents I-1˜I-N to be generated between the first node N1and the second node N2. The branch currents I-1˜I-N respectively flow through the fuses F-1˜F-N so that one of the fuses F-1˜F-N is blown out by the branch current flowing through the one of the fuses F-1˜F-N. In greater detail, when the branch currents I-1˜I-N flow through fuses F-1˜F-N respectively, the fuse having the smallest resistance value among the fuses F-1˜F-N will correspond to the branch current having the greatest current value, the fuse having the smallest resistance value among the fuses F-1˜F-N is thus blown out because the corresponding branch current having the greatest current value exceeds a critical value tolerable for the fuse having the smallest resistance value. It is noted that the number of the branch currents I-1˜I-N corresponds to the number of the fuses F-1˜F-N. In other words, the number of the branch currents I-1˜I-N is the same as the number of the fuses F-1˜F-N.

In another embodiment, as shown inFIG. 1B, the fuse circuit100may further include a switch control circuit103. The switch control circuit103is configured for selectively controlling the switches S-1˜S-P to allow one of the trimming components101-1˜101-P to be conducted with the fuses F-1˜F-N. In greater detail, the switch control circuit103transmits a switch control signal102to the switches S-1˜S-P to allow one of the switches S-1˜S-P to receive the switch control signal102and allow one of the trimming components101-1˜101-P to be conducted with the fuses F-1˜F-N according to the switch control signal102. When one of the trimming components101-1˜101-P is conducted to the fuses F-1˜F-N, the conducted trimming component allows the branch currents I-1˜I-N to be generated between the first node N1and the second node N2, and the branch currents I-1˜I-N respectively flow through fuses F-1˜F-N to trim the fuses F-1˜F-N.

FIG. 2depicts a schematic diagram of a fuse circuit200according to still another embodiment of this invention. Since the fuse circuit200of the present embodiment is similar to the fuse circuit100, only the difference between the fuse circuit200and the fuse circuit100is described as follows.

As shown inFIG. 2, the fuse circuit200further includes a control circuit201configured for generating a control signal202to trigger the trimming components101-1˜101-P.

For example, each of the trimming components101-1˜101-P includes a silicon control rectifier (SCR), a metal oxide semiconductor (MOS) device, a low-voltage triggering silicon control rectifier (LVTSCR), or a trimming circuit. When the trimming component is a silicon control rectifier, only a short pulse signal is required to achieve triggering, e.g., 1000 nanoseconds. When a metal oxide semiconductor device is used as the trimming component, a pulse signal having a longer duration is required to turn on the metal oxide semiconductor device, e.g., 10 microseconds. It is noted that the above trimming components are only for explanation of aspects of the present embodiment and are not intended to limit the present invention. Any component capable of trimming the fuse is within the scope of the present invention.

Additionally, a proper component can be selected to serve as the trimming components101-1˜101-P depending on circuit designs according to the present invention. The control circuit201transmits the control signal202to the trimming components101-1˜101-P to trigger the trimming components101-1˜101-P so as to generate the branch currents I-1˜I-N. The fuses F-1˜F-N are thus trimmed. In practical applications, the switch control circuit103and the control circuit201can generate signals synchronously. In other words, when one of the switches S-1˜S-P is turned on, the trimming component corresponding to the one of the switches S-1˜S-P is triggered at the same time point.

In another practical application, the switch control circuit103and the control circuit201can generate signals asynchronously. In other words, once one of the switches S-1˜S-P is turned on, the trimming component corresponding to the one of the switches S-1˜S-P is triggered at a delayed time point.

FIG. 3Adepicts a schematic diagram of a fuse circuit300according to yet another embodiment of this invention. Since the fuse circuit300of the present embodiment is similar to the fuse circuit200, and the fuse circuits200and300include the same components, a description in this regard is not provided.

To simplify the matters, the number N here is set to two. That is, the fuse circuit300includes the fuse F-1and the fuse F-2, in which the fuse F-1is set to be a metal fuse and the fuse F-2is set to be a polysilicon fuse. It is noted that the above-mentioned numbers and materials of the fuses are only for explanation of aspects of the present embodiment and are not intended to limit the present invention.

As shown inFIG. 3A, the switch S-1is set to be turned on to allow the trimming component101-1to be coupled to the fuse F-1and the fuse F-2. In the present embodiment, the trimming component101-1is set to be a low-voltage triggering silicon control rectifier that includes a silicon control rectifier and a metal oxide semiconductor device. It is noted that since the switch S-1is in a conducting state and the other switches S-2˜S-P are in a non-conducting state, inFIG. 3Aonly the conducting state of the switch S-1is depicted and the non-conducting state of the other switches S-2˜S-P is not depicted.

To simplify the matters, a description is provided as follows by taking the fuse F-1to be a metal fuse and the fuse F-2to be a polysilicon fuse as an example. When the fuse F-1is a metal fuse and the fuse F-2is a polysilicon fuse, the resistance value of the fuse F-1is approximately 0.1 ohm and the resistance value of the fuse F-2is approximately 100 ohms.

With respect to the operations, in a first state, the control circuit201does not generate the control signal202and the trimming component101-1does not act. At this time, the fuse F-1(such as the metal fuse) and the fuse F-2(such as the polysilicon fuse) are coupled in parallel to the first node N1and the second node N2. A total resistance value of the metal fuse and the polysilicon fuse is approximately 0.1 ohm.

In a second state, the control circuit201generates the control signal202. The control signal202includes a pulse signal. The control circuit201activates the silicon control rectifier by transmitting a pulse signal having a short duration to trigger the silicon control rectifier in the low-voltage triggering silicon control rectifier. In the present embodiment, the metal fuse has a smaller resistance value when compared with the polysilicon fuse. Hence, the branch current I-2flowing through the polysilicon fuse has a smaller current value and the branch current I-1flowing through the metal fuse has a greater current value. Under the circumstances, the branch current I-1flowing through the metal fuse has the current value exceeding a critical value tolerable by the metal fuse, the metal fuse is thus blown out and generates a new resistance value.FIG. 3Bis a schematic diagram showing relationships between fuse resistance values and a pulse signal. When the fuses F-1and F-2are trimmed the first time, the pulse signal transmitted has a duration of approximately 100 nanoseconds. The resistance value of the metal fuse increases to approximately 100K ohms and the resistance value of the polysilicon fuse is still approximately 100 ohms. Under the circumstances, a new total resistance value of the metal fuse and the polysilicon fuse is approximately 100 ohms.

In a third state, the control circuit201re-generates the control signal202so that the trimming component101-1is re-activated. The control signal202generated by the control circuit201is a pulse signal having a longer duration so as to trigger the metal oxide semiconductor device in the low-voltage triggering silicon control rectifier. The metal oxide semiconductor device is thus activated. For example, in the embodiment shown inFIG. 3B, the control circuit201uses the pulse signal having the duration of 2000 nanoseconds to trigger the metal oxide semiconductor device in the low-voltage triggering silicon control rectifier. According to the present embodiment, the new resistance value of the metal fuse is greater than the resistance value of the polysilicon fuse, the branch current I-1flowing through the metal fuse thus has a current value smaller than that of the branch current I-2flowing through the polysilicon fuse. In practical applications, the branch current I-2flowing through the polysilicon fuse has the current value exceeding a critical value tolerable by the polysilicon fuse, the polysilicon fuse is thus blown out and generates a new resistance value which is approximately 1M ohms. Under the circumstances, a new total resistance value of the metal fuse and the polysilicon fuse is approximately 100K ohms because the resistance value of the metal fuse is 100K ohms and the new resistance value of the polysilicon fuse is 1M ohms. In this manner, the total resistance values in the first state, the second state, and the third state are respectively 0.1 ohm, 100 ohms, and 100K ohms, and the multiple relationships between the resistance values in the first and second states and in the second and third states are approximately 1000 times.

FIG. 3Cdepicts a schematic diagram of a fuse circuit400according to another embodiment of this invention. Since the fuse circuit400of the present embodiment is similar to the fuse circuit300and part of the components in the fuse circuits300,400are the same, a description in this regard is not provided.

Different fromFIG. 3A, only the trimming component101-2, the trimming component101-3, and the switch S-2and the switch S-3corresponding to the trimming component101-2and the trimming component101-3are depicted inFIG. 3C, other switches and trimming components are not depicted. In the present embodiment, the trimming component101-2is set to be a silicon control rectifier. The trimming component101-3is set to be a metal oxide semiconductor device.

With respect to the operations inFIG. 3C, first, the switch S-2is set to be turned on so that the trimming component101-2is coupled to the fuse F-1and the fuse F-2.

To simplify the matters, a description is provided as follows by taking the fuse F-1to be a metal fuse and the fuse F-2to be a polysilicon fuse for example. When the fuse F-1is a metal fuse and the fuse F-2is a polysilicon fuse, the resistance value of the fuse F-1is approximately 0.1 ohm and the resistance value of the fuse F-2is approximately 100 ohms.

With respect to the operations, in a first state, the control circuit201does not generate a control signal204and206, so that the trimming component101-2does not act. At this time, the fuse F-1(such as the metal fuse) and the fuse F-2(such as the polysilicon fuse) are coupled in parallel to the first node N1and the second node N2. A total resistance value of the metal fuse and the polysilicon fuse is approximately 0.1 ohm.

In a second state, the control circuit201generates the control signal204at a first time. The control signal204includes a pulse signal. The control circuit201triggers the silicon control rectifier by transmitting a pulse signal having a short duration so that the silicon control rectifier is activated. In the present embodiment, the metal fuse has a smaller resistance value when compared with the polysilicon fuse. Hence, the branch current I-2flowing through the polysilicon fuse has a smaller current value and the branch current I-1flowing through the metal fuse has a greater current value. Under the circumstances, the branch current I-1flowing through the metal fuse has the current value exceeding a critical value tolerable by the metal fuse, the metal fuse is thus blown out and generates a new resistance value. The relationships between the fuse resistance values and the pulse signal is shown inFIG. 3B. When the fuses F-1and F-2are trimmed the first time, the pulse signal transmitted has a duration of approximately 100 nanoseconds. The resistance value of the metal fuse increases to approximately 100K ohms and the resistance value of the polysilicon fuse is still approximately 100 ohms. Under the circumstances, a new total resistance value of the metal fuse and the polysilicon fuse is approximately 100 ohms.

After that, the switch S-2is set not to be turned on and the switch S-3is set to be turned on by the switch control circuit103(not shown inFIG. 3C). Hence, the trimming component101-3is coupled to the fuse F-1and the fuse F-2.

In a third state, the control circuit201generates the control signal206at a second time so that the trimming component101-3is activated. The control signal206generated by the control circuit201is a pulse signal having a longer duration to trigger the metal oxide semiconductor device so that the metal oxide semiconductor device is activated. In the present embodiment, the new resistance value of the metal fuse is greater than the resistance value of the polysilicon fuse, the branch current I-1flowing through the metal fuse thus has a current value smaller than that of the branch current I-2flowing through the polysilicon fuse. In practical applications, the branch current I-2flowing through the polysilicon fuse has the current value exceeding a critical value tolerable by the polysilicon fuse, the polysilicon fuse is thus blown out and generates a new resistance value that is approximately 1M ohms. Under the circumstances, a new total resistance value of the metal fuse and the polysilicon fuse is approximately 100K ohms because the resistance value of the metal fuse is 100K ohms and the new resistance value of the polysilicon fuse is 1M ohms.

In short, the control circuit201generates the control signal204at the first time to trigger the silicon control rectifier. Then, after a delay time, the control circuit201generates the control signal206at the second time to trigger the metal oxide semiconductor device. In other words, the second time is later than the first time. Additionally, the width of the pulse signal that serves as the control signal204is greater than the width of the pulse signal that serves as the control signal206.

In this manner, the total resistance values obtained in the first state, the second state, and the third state are respectively 0.1 ohm, 100 ohms, and 100K ohms according to the above embodiment, and multiple relationships between the resistance values in the first and second states and in the second and third states are approximately 1000 times.

In one embodiment, since using different materials to fabricate the fuses F-1˜F-P makes the multiple relationships between their resistance values range from 10 times to 1000 times, the fuses F-1˜F-P made from different materials are fabricated as different layers on a substrate by deposition.FIG. 4is a cross-sectional view of a plurality of fuses according to one embodiment of this invention. For example, as shown inFIG. 4, the fuse F-1and the fuse F-2are made from different materials. The fuse F-1and the fuse F-2are stacked on the substrate402in sequence. The fuse F-1and the fuse F-2are fabricated as different layers and are isolated by an insulating layer404and an insulating layer406. It is noted that the above-mentioned numbers of the fuses and the insulating layers are only for explanation of aspects of the present embodiment and are not intended to limit the present invention.

FIG. 5depicts a schematic diagram of a fuse circuit500according to still another embodiment of this invention. Since the fuse circuit500of the present embodiment is similar to the fuse circuit300and part of the components in the fuse circuits300and500are the same, only the difference between the fuse circuit300and the fuse circuit500is described.

As shown inFIG. 5, the difference between the fuse circuit300and the fuse circuit500lies in that the fuse circuit500does not include the switches S-1˜S-P and the switch control circuit103. In greater detail, the fuse circuit500includes the fuse F-1, the fuse F-2, the control circuit201, and a low-voltage triggering silicon control rectifier501. The low-voltage triggering silicon control rectifier501is a trimming component of the fuse circuit500. To simplify the matters, the fuse F-1is set to be a metal fuse and the fuse F-2is set to be a polysilicon fuse. Under the circumstances, the resistance value of the fuse F-1is approximately 0.1 ohm, and the resistance value of the fuse F-2is approximately 100 ohms. It is noted that the above-mentioned numbers and materials of the fuses are only for explanation of aspects of the present embodiment and are not intended to limit the present invention.

With respect to the operations, in a first state, the control circuit201does not generate the control signal202so that the low-voltage triggering silicon control rectifier501does not act. In addition, the fuse F-1(such as the metal fuse) and the fuse F-2(such as the polysilicon fuse) are coupled in parallel to the first node N1and the second node N2. A total resistance value of the metal fuse and the polysilicon fuse is approximately 0.1 ohm.

In a second state, the control circuit201generates the control signal202to trigger the low-voltage triggering silicon control rectifier501so that a silicon control rectifier in the low-voltage triggering silicon control rectifier501is triggered by a pulse signal that serves as the control signal202at a first time. When the fuses F-1and F-2are trimmed the first time, the pulse signal transmitted by the control circuit201has a duration of approximately 100 nanoseconds. The resistance value of the metal fuse increases to approximately 100K ohms and the resistance value of the polysilicon fuse is still approximately 100 ohms. Under the circumstances, a new total resistance value of the metal fuse and the polysilicon fuse is approximately 100 ohms.

In a third state, the control circuit201generates the control signal202to trigger the low-voltage triggering silicon control rectifier501so that a metal oxide semiconductor device in the low-voltage triggering silicon control rectifier501is triggered by a pulse signal that serves as the control signal202at a second time. When the fuses F-1and F-2are trimmed the second time, the pulse signal transmitted by the control circuit201has a duration of approximately 2000 nanoseconds. The resistance value of the polysilicon fuse thus increases to approximately 1M ohms. Under the circumstances, a new total resistance value of the metal fuse and the polysilicon fuse is approximately 100K ohms because the resistance value of the metal fuse is 100K ohms and the new resistance value of the polysilicon fuse is 1M ohms. In this manner, the total resistance values in the first state, the second state, and the third state are respectively 0.1 ohm, 100 ohms, and 100K ohms, and the multiple relationships between the resistance values in the first and second states and in the second and third states are approximately 1000 times.

According to the above embodiments, it is understood that a plurality of fuses and a single trimming component or a plurality of fuses and a plurality of trimming components constitute the fuse circuit in the present invention. A specific trimming component is selected and a proper pulse signal is transmitted to trim the fuses. In addition, the fuses have different resistance values, in which the fuse having the smallest resistance value is blown out by the trimming current generated by the activated trimming component. Hence, two or more than two resistance values can be achieved through multiple time programming.