Abstract: An apparatus for regulating eFUSE programming current includes a current control generator receiving an input reference current through a first current path of reference fuses, the input reference current proportional to a desired eFUSE programming current; a second current path including a reference programming FET and a second group of reference fuses; and a voltage comparator coupled to a gate terminal of the reference programming FET so as to adjust the gate voltage of the reference programming FET to equalize a first voltage across the first current path with a second voltage across the second current path. The gate voltage of the reference programming FET is an output of the current control generator, coupled to corresponding gates of one or more selected programming devices of an eFUSE array such that the selected programming devices source the desired eFUSE programming current to a selected eFUSE to be programmed.

Abstract: Provided are an electrical fuse device and a method of operating the same. The electrical fuse device may include a fuse, and a driving element connected to the fuse and including a resistance change layer having a resistance that changes according to an applied voltage. The resistance change layer may have a metal-insulator transition (MIT) characteristic. As the driving element is turned on, a programming current may be applied to the fuse connected to the driving element.

Abstract: An eFuse (electronic fuse) circuit has a first detector for determining whether an ESD (electrostatic discharge) event occurs at a circuit pad of an integrated circuit and provides an ESD trigger signal in response thereto. A second detector detects a presence of a first power supply voltage and provides a power on signal indicating the presence of the first power supply voltage. A fuse is permitted to be programmable when no detection of the ESD event occurs and at the same time a presence of the power on signal is detected. The fuse is not permitted to be programmed when an ESD event is detected or when there is an absence of the power on signal. An array of fuses is thereby protected from inadvertent programming from an ESD event or powering up an integrated circuit.

Abstract: A voltage divider circuit generating a divided voltage by dividing an input voltage with a predetermined voltage division ratio, and outputting the divided voltage is disclosed. The voltage divider circuit includes a first resistor circuit including multiple resistors connected in series, the resistors being connected in parallel to corresponding fuses; and a second resistor circuit including multiple resistors connected in series, the resistors being connected in parallel to corresponding fuses, the second resistor circuit being connected in series to the first resistor circuit. The divided voltage is output from the connection of the first resistor circuit and the second resistor circuit, and the fuses of the first resistor circuit and the second resistor circuit are subjected to trimming so that the combined resistance of the first resistor circuit and the second resistor circuit is constant.

Abstract: The invention provides an electrical fuse device comprising: a plurality of fuse cores, each having an electrical fuse element and a switching element serially connected to the electrical fuse element; a program control circuit generating a program shift signal by sequentially shifting a program control transmission signal in synchronization with an effective program clock signal and subsequently generating a program signal to be sent to each of the switching elements in the plurality of fuse cores based on program data and the program shift signal; and a program clock control circuit controlling the conducting and non-conducting states of a program clock signal in accordance with a program clock enable signal and, when the program clock signal is in a conducting state, transmitting the program clock signal to the program control circuit as the effective program clock signal.

Abstract: A method and system is disclosed for protecting electrical fuse circuitry. A electrical fuse circuit with electrostatic discharge (ESD) protection has at least one electrical fuse, a programming device coupled in series with the electrical fuse having at least a transistor for receiving a control signal for controlling a programming current flowing through the electrical fuse, a voltage source coupled to the fuse and the programming device for providing the programming current, and a protection module coupled to a gate of the transistor at its first end for reducing charges accumulated at the gate of the transistor due to electric static charges arriving at the voltage source, thereby preventing the programming device from accidentally programming the fuse.

Abstract: One-time programmable (OTP) nonvolatile fuse memory cells are disclosed that do not require decoding or addressing for reading their data content. Each fuse memory cell has its content latched at its output and available at all times and can be used, for example, for code storage memories, serial configuration memories, and as individual fuse bits for ID (identification), trimming, and other post-fabrication System-on-Chip (SoC) customization needs.

Abstract: Provided are an antifuse and methods of operating and manufacturing the same. The antifuse may include first and second conductors separate from each other; a dielectric layer for an antifuse between the first and second conductors; and a diffusion layer between one of the first and second conductors and the dielectric layer.

Abstract: A master fuse module includes a base housing configured to be disposed on a battery, a fuse assembly connected to the base housing, and a cover disposed on the base housing. The fuse assembly includes a first generally planar portion including a first terminal, a second generally planar portion disposed generally perpendicular to the first generally planar portion, a plurality of second terminals, and a plurality of fuses. Each fuse includes a first portion in electrical communication with the first terminal and a second portion in electrical communication with one of the plurality of second terminals. A fuse element is in electrical communication between the first and second portions and provides overcurrent protection by melting when subjected to a predetermined current. A plurality of connectors connects the fuse assembly to the base housing.

Abstract: Provided may be a multi-level anti-fuse and methods of fabricating and operating the same. The multi-level anti-fuse may include at least three anti-fuses having a plurality of anti-fuses connected in parallel constituting a parallel connection structure and at least one anti-fuse connected to the parallel connection structure in series, wherein the parallel connection structure may have a smaller resistance than the resistance of the anti-fuse connected in series, the plurality of anti-fuses connected in parallel may include dielectric layers having different thicknesses from one another, and the breakdown voltages of each dielectric layer may be different from one another.

Abstract: A method of forming a carbon nanotube fuse by depositing a carbon nanotube layer, then depositing a cap layer directly over the carbon nanotube layer. The cap layer is formed of a material that has an insufficient amount of oxygen to significantly oxidize the carbon nanotube layer under operating conditions, and is otherwise sufficiently robust to protect the carbon nanotube layer from oxygen and plasmas. A photoresist layer is formed over the cap layer, and the photoresist layer is patterned to define a desired size of fuse. Both the cap layer and the carbon nanotube layer are completely etched, without removing the photoresist layer, to define the fuse having two ends in the carbon nanotube layer. Just the cap layer is etched, without removing the photoresist layer, so as to reduce the cap layer by a desired amount at the edges of the cap layer under the photoresist layer, without damaging the carbon nanotube layer.

Abstract: A trimmer device for adjusting a reference signal of a target circuit is disclosed. The trimmer device includes: a switch controlling module and an impedance adjustment circuit. The switch controlling module includes: a fuse, selectively being melted according to the reference signal; and a control signal generating circuit, for generating a control signal according to the melting condition of the fuse. The impedance adjustment circuit includes: a switch module, being selectively conductive according to the control signal; and an impedance network, for determining an equivalent impedance of the impedance network according to the conducting condition of the switch module to further adjust the reference signal.

Abstract: A trimming circuit is disclosed. The trimming circuit includes a first trimming circuit having resistors and fuses, and a second trimming circuit having a resistor, an NMOS transistor, and a control circuit. The control circuit includes an inverter circuit and a series circuit in which a resistor and fuses are connected in series. The first trimming circuit is connected with a reference resistor in series and the second trimming circuit is connected with the reference resistor in parallel.

Abstract: An electrical fuse including a polysilicon layer; a silicide layer formed over the polysilicon layer; and a first metal contact and a second metal contact arranged over the silicide layer, while being spaced from each other, the electrical fuse being configured so that the silicide layer, after disconnection, is excluded from a region right under the second metal contact, and from a region between the second metal contact and the first metal contact is provided.

Abstract: A fuse circuit for a semiconductor integrated circuit includes a control unit configured to activate a fuse set control signal in response to an external command signal, and a plurality of fuse sets, each configured so that power is supplied to internal fuses in response to the activation of the fuse set control signal.

Abstract: A binary bidirectional trimming circuit is disclosed. The trimming circuit includes: a first resistor set having 4 resistors in parallel connected and a first fuse bridged two ends thereto provide one trimming step; a second resistor set having 2 resistors in series connected and a second fuse bridged two ends thereto provide eight trimming steps; a third resistor set having 2 resistors in parallel connected and a third fuse bridged two ends thereto provide two trimming steps; a fourth resistor set having 1 resistor and a fourth fuse bridged two ends thereto provide four trimming steps; a first loading resistor; and a second loading resistor. The first resistor set, second resistor set, first loading resistor, third resistor set, the fourth resistor set, and the second loading resistor are in series connected.

Abstract: A circuit adjustable after packaging includes a functional circuit supplied with a power potential and a reference potential and has at least one parameter adjustable by programming at least one programmable element and a circuit to program the programmable element of the functional circuit. The adjustable circuit also includes a limiter circuit to limit the voltage between the power supply potential and the reference potential to an adjustable limiting voltage, and a circuit to adjust the limiting voltage. After adjusting a parameter of the functional circuit, the limiting voltage of the limiter circuit is adjusted.

Abstract: A method and circuit for implementing eFuse resistance screening, and a design structure on which the subject circuit resides are provided. An eFuse is sensed using a first reference resistor. Responsive to the eFuse being sensed as blown with the first reference resistor, the eFuse is sensed using a second reference resistor having a higher resistance than the first reference resistor. Responsive to the eFuse being sensed as unblown with the second reference resistor, the eFuse is recorded as poorly blown. Reliability concerns are identified quickly and accurately without being required to measure the resistance of the eFuse.

Abstract: The fuse circuit includes a first program unit, a second program unit and a sensing circuit. The first and second program units are programmed simultaneously. The first program unit is programmed in a program mode in response to a fuse program signal and outputs a first signal in a sensing mode, such that the first signal increases when the first program unit is programmed. The second program unit is programmed in the program mode in response to the program signal and outputs a second signal in the sensing mode, such that the second signal decreases when the second program unit is programmed. The sensing circuit generates a sensing output signal in response to the first and second signals, such that the sensing output signal indicates whether or not the program units are programmed.

Abstract: In a semiconductor circuit device including a first terminal adapted to receive a first voltage and a second terminal adapted to receive a second voltage lower than the first voltage, a capacitive circuit and a short-circuit preventing circuit are provided in series between the first and second terminals. In this case, when the capacitive element is in an insulating (non-conductive) state, the short-circuit preventing circuit is in a conductive state, while, when the capacitive circuit is in a conductive state, the short-circuit preventing circuit is in an insulating state.

Abstract: A semiconductor device employs two electric fuses (31, 32) connected in parallel to each other. First terminals of the electric fuses (31, 32) are connected to a junction of first and second P-channel transistors (21, 22), which are connected in series between a high potential application line (111) and a ground, and connected to a third P-channel transistor (23). Second terminals of the electric fuses (31, 32) are connected to a low potential application line (121). When an extra-high voltage is applied between the first and second terminals of the electric fuses (31, 32), a breakdown connection is produced in at least one of the electric fuses (31, 32). Thus, 1-bit information is written into the semiconductor device.

Abstract: A fuse-fetching circuit comprises a plurality of fuses, a plurality of first switches and a shift register. Each of the first switches includes a first data end, a second data end and a control end. The first data end is connected to the fuse, and the control end is controlled by a fuse-fetching signal. The shift register includes a plurality of registers, each of which includes a first latch, a first transmission gate, a second latch and a second transmission gate. The first latch is connected to the second data end of the first switch.

Abstract: An electronic device with polarity reversal protected connections and irreversibly interruptible programming connections, wherein the interruption is performed through safety elements provided in the programming paths, behind which safety elements diodes are disposed which block towards ground in normal operation, so that an overload current can be passed through the safety elements and through the diodes to ground through intentional polarity reversal of the respective connections, whereby the safety elements are destroyed and the programming conductors are irreversibly interrupted.

Abstract: The present invention discloses a bias circuit for a sense amplifier having a device under sensing, the device under sensing having an un-programmed state and a programmed state, the bias circuit comprises at least one first branch having at least one first device formed substantially the same as the device under sensing and remaining in the un-programmed state, and at least one second device formed also substantially the same as the device under sensing and being in the programmed state, wherein the at least one first device and the at least one second device are serially connected. A typical application of the present invention is an electrical fuse memory.

Abstract: A fuse circuit of a semiconductor integrated apparatus includes a first fuse block and a second fuse block. The first fuse block includes a first up fuse block that includes a plurality of fuses, and a first down fuse block that includes fuses less than the number of fuses of the first up fuse block. The second up fuse block includes a second up fuse block that includes the same number of fuses as the first down fuse block, and a second down fuse block that includes the same number of fuses as the first up fuse block. Structures of the first up fuse block and the first down fuse block are asymmetric, and the structures of the second up fuse block and the second down fuse block are asymmetric.

Abstract: A circuit that employs an anti-tamper sensor includes a circuit element that is responsive to a first input and to a second input. A selective coupling element couples the circuit element to the first input and is responsive to the anti-tamper sensor. The selective coupling element has a first state that allows the circuit element to operate normally when the anti-tamper sensor does not detect a tamper condition and is configured to enter a second state that causes the circuit element to become inoperable when the anti-tamper sensor detects a tamper condition. A decoy coupling element is disposed between the second input and the circuit element and has an appearance corresponding to the selective coupling element. The decoy coupling element will cause the circuit element not to operate normally if the decoy coupling element has a selected physical property of the selective coupling element in the first state.

Abstract: A skew signal generator is provided which comprises a fuse signal generating unit for generating a plurality of fuse signals, and an encoder for generating skew signals including skew information of a wafer by encoding the fuse signals.

Abstract: Disclosed is a design structure of an apparatus incorporating a detection circuit adapted for determining the state of selected fuses and a programming circuit for blowing selected fuses on demand. Also, disclosed are embodiments of an associated method. The detection circuit comprises a plurality of fuses in identical signal and reference legs in order to increase the signal margin for detecting blown fuses and/or current sources configured to pass offset currents through the signal and reference legs in order to set the trip point for detecting blown fuses between the un-blown and the minimum blown resistances. Thus, the invention provides the flexibility of single-sided fuse state detection devices with even greater sensitivity than both single-sided and differential fuse state detection device.

Abstract: The present invention, generally speaking, provides for a non volatile memory cell requiring no extra process steps. In one embodiment, the non volatile memory cell is a lateral polysilicon programmable read only memory cell, in particular a lateral poly fuse memory cell. Technique are provided to achieve a high yielding, voltage, temperature, and process insensitive lateral poly fuse memory. In one embodiment, a fusible link memory circuit includes a fusible link memory element and a programming circuit. The programming circuit includes a replica of the fusible link memory element and a programming current source for producing a known current density in the fusible link memory element in spite of variations including at least process variations.

Abstract: Disclosed is a design structure for systems and methods of managing a set of programmable fuses on an integrated circuit.

Abstract: The present invention relates to an anti-fuse repair control circuit which regulates transmission of a power voltage and a back-bias voltage that are converted to repair an anti-fuse to a circuit part. As such, the present invention prevents the influence of a high power voltage or a low back-bias voltage on a circuit part such as a cell, a peripheral circuit, or a core region during an anti-fuse repair. The anti-fuse repair control circuit includes an anti-fuse repair enabling part providing an anti-fuse repair enabling signal corresponding to a repair of an anti-fuse; a power voltage control part controlling transmission of a power voltage to a first circuit part according to an enablement state of the anti-fuse repair enabling signal; and a back-bias voltage control part controlling transmission of a back-bias voltage to a second circuit part according to the enablement state of the anti-fuse repair enabling signal.

Abstract: A circuit for programming an antifuse coupled between a first node and a second node includes at least one transistor for supplying a programming potential VPP to the first node. A first transistor has a source coupled to a third node switchably coupleable between a potential of VPP/2 and ground potential, a drain, and a gate. A second transistor has a source coupled to the drain of the first transistor, a drain coupled to the second node, and a gate. Programming circuitry is coupled to the gate of the first transistor and the gate of the second transistor and configured to in a programming mode apply a potential of either zero volts or VPP/2 to the gate of the first transistor and to apply a potential of VPP/2 to the gate of the second transistor. The first and second transistors have a BVDss rating of not more than about VPP/2.

Abstract: The fuse cell architecture 371 for the presently claimed invention employs a multiple fuse structure 301, 302 architecture in lieu of a single fuse structure. As such, the terminals of these fuse structures that couple to other on-chip devices are always at ground potential throughout the application of programming voltage to the fuse pads 311. This approach overcomes previous single fuse problems owing to the fact that a sufficiently high programming voltage can be applied to blow fuse structures with unexpectedly high resistance without damaging nearby on-chip devices. Furthermore, even if one of the fuse structures 301, 302 possessed an abnormally high resistance which would not be blown under typical conditions, the desired circuit trimming result can still be achieved owing to the blowing of the other fuse structure in the fuse cell 371.

Abstract: A fuse option circuit including a fuse, a control switch, a latch, and a logical operational controller is provided. The latch stores a selected level. The logical operational controller outputs a selected result signal and feedbacks a control signal to the control switch. The level of the control signal determines whether the control switch is on or off. Therefore, the required level is input to the latch and the working mode having an ultra low current is selected. Furthermore, when the fuse is in an untrimmed state, the level of the selected result signal could be selected by a reset pulse signal of the latch in order to test a product. Afterward, it is determined whether the fuse is trimmed or not. When the fuse is in a trimmed state, the level of the selected result signal is established by a rising edge of the reset pulse signal.

Abstract: A design structure for an apparatus for programming an electronically programmable semiconductor fuse. The apparatus applies a programming current to a fuse link as a series of multiple pulses. Application of the programming current as a series of multiple short pulses provides a level of programming current sufficiently high to ensure reliable and effective electromigration while avoiding exceeding temperature limits of the fuse link.

Abstract: A design structure for electrically programmable fuse sense circuit having an electrically programmable fuse and a reference resistance. A first current source is coupled, through a first switch, to the electrically programmable fuse. A second current source is coupled, through a second switch, to the reference resistance. A precharge signal enables the first current source, the second current source and closes the first switch and the second switch, creating voltage drops across the electrically programmable fuse and the reference resistance. When the precharge signal goes inactive, the first current source and the second current source are shut off, and, at the same time the first switch and the second switch are opened. A latching circuit uses a difference in the voltage drops when the precharge signal goes inactive to store a state of the electrically programmable fuse, indicative of whether the electrically programmable fuse is blown or unblown.

Abstract: A fuse option circuit including a fuse, a control switch, a latch, and a logical operational controller is provided. The latch stores a selected level. The logical operational controller outputs a selected result signal and feedbacks a control signal to the control switch. The level of the control signal determines whether the control switch is on or off. Therefore, the required level is input to the latch and the working mode having an ultra low current is selected. Furthermore, when the fuse is in an untrimmed state, the level of the selected result signal could be selected by a reset pulse signal of the latch in order to test a product. Afterward, it is determined whether the fuse is trimmed or not. When the fuse is in a trimmed state, the level of the selected result signal is established by a rising edge of the reset pulse signal.

Abstract: A fuse-fetching circuit comprises a plurality of fuses, a plurality of first switches and a shift register. Each of the first switches includes a first data end, a second data end and a control end. The first data end is connected to the fuse, and the control end is controlled by a fuse-fetching signal. The shift register includes a plurality of registers, each of which includes a first latch, a first transmission gate, a second latch and a second transmission gate. The first latch is connected to the second data end of the first switch.

Abstract: An antifuse element includes a plurality of MOS transistors; a first electrode to which source electrodes of the plurality of MOS transistors are commonly connected; a second electrode to which gate electrodes of the plurality of MOS transistors are commonly connected; a third electrode to which at least one of drain electrodes of the plurality of MOS transistors is capable of being connected; and an insulation film provided between the drain electrodes of the plurality of MOS transistors and the third electrode, wherein the insulation on at least one position in said insulation film and that corresponds to one of the drain electrodes is broken down.

Abstract: An electrical fuse determination circuit that can speedily and reliably incorporate an electrical fuse data and improve a reliability of electrical fuse device, includes a first electrical fuse device of which one end connects with a higher voltage, a second electrical fuse device of which one end connects with a lower voltage, a set portion that puts one of the first electrical fuse device and the second electrical fuse device in a conductive state, and a determination portion that determines a voltage level of a predetermined contact point connecting the other end of the first electrical fuse device and the other end of the second electrical fuse device.

Abstract: A electrically programmable fuse sense circuit having an electrically programmable fuse and a reference resistance. A first current source is coupled, through a first switch, to the electrically programmable fuse. A second current source is coupled, through a second switch, to the reference resistance. A precharge signal enables the first current source, the second current source and closes the first switch and the second switch, creating voltage drops across the electrically programmable fuse and the reference resistance. When the precharge signal goes inactive, the first current source and the second current source are shut off, and, at the same time the first switch and the second switch are opened. A latching circuit uses a difference in the voltage drops when the precharge signal goes inactive to store a state of the electrically programmable fuse, indicative of whether the electrically programmable fuse is blown or unblown.

Abstract: A fuse circuit comprises at least one fuse circuit unit and a current blocking module. The fuse circuit unit comprises a voltage establishing module and a latch. The voltage establishing module is coupled to a first reference voltage source and includes a fuse that is capable of being selectively blown according to an initial setting signal. The fuse has a first terminal coupled to a node and a second terminal. The voltage establishing module establishes a voltage level on the node according to the blown-off status of the fuse. The latch is coupled to the voltage establishing module through the node for latching the voltage level of the node and generating the output signal. The current blocking module is coupled between a second reference voltage source and the second terminal of the fuse for blocking the current flowing through the fuse while initial setting.

Abstract: A fuse sensing circuit includes a sense controller and a fuse state sensor. The sense controller includes a reference fuse and a reference sensor coupled to the reference fuse. The reference sensor generates a sample clock with a certain threshold transition characteristic in response to the assertion of a sense input by detecting a programming state of the reference fuse. The fuse state sensor includes a sample fuse, a fuse sensor coupled to the sample fuse, and a flip-flop. The sample fuse is configured to generate a data signal indicative of a programming state of the sample fuse when an enable input is asserted and the sense input is asserted. The flip-flop is configured to sample the data signal using the threshold transition characteristic on an assertion edge of the sample clock. The fuse sensing circuit may be included in an image sensor or an imaging system.

Abstract: Methods and circuitry for reducing ground bounce and VCC sag effects in integrated circuit (“IC”) devices is provided. In particular, a via-programmable design for I/O circuitry in IC devices is provided. The via-programmable I/O circuitry is used to disconnect I/O pin driver circuitry from and create a substantially direct connection between unused I/O pins and the ground and/or VCC signals of an IC device to reduce ground bounce and VCC sag, respectively.

Abstract: In one embodiment, a integrated circuit (IC) configurable to have any one of a plurality of different feature sets, the IC including (a) one or more feature blocks adapted to be independently enabled or disabled, (b) a one-time-programmable (OTP) memory cell for each feature block, the OTP memory cell storing a value, and (c) a feature control module for each feature block, each feature control module connected between the corresponding OTP memory cell and the corresponding feature block, and adapted to enable or disable the corresponding feature block based on the value stored in the corresponding OTP memory cell. The OTP memory cells are programmed by a vendor to select the particular feature set for the IC which is to be available to a purchaser.

Abstract: A semiconductor integrated circuit device including a fuse latch circuit including a fuse and a latch circuit for latching fuse data held in the fuse, a fuse counter circuit for counting the number of transfers of the fuse data, and a control circuit including a transmitter circuit for transmitting the fuse data to the outside, and a detour data path circuit which when the fuse data is not transferred, does not transfer the fuse data to the outside, and forms a detour data path for detouring the fuse data in the circuit itself.

Abstract: A signature circuit in a semiconductor chip includes a signature program circuit configured to be programmed with signature information and to output a signature signal in response to the signature information; a signature output circuit configured to block the signature signal output by the signature program circuit during operation in a normal mode, and configured to pass the signature signal during operation in a test mode; and a pad-driving transistor directly coupled to the pad, configured to drive the pad during operation in the normal mode in response to an operation command, and configured to drive the pad during operation in the test mode in response to the signature signal output by the signature output circuit. The signature circuit outputs the signature information through a transistor for adjusting impedance to reduce a chip size by omitting an additional logic circuit for the signature circuit.

Abstract: An integrated circuit device having at least one fuse capable of being blown in order to provide measurements of fuse current-voltage characteristics is provided. The integrated circuit device also provides at least one pulse generation circuit associated with the fuse and capable of generating a pulse to blow the fuse through one or more DC input signals.

Abstract: An eFuse sensing circuit replaces the inverters used to provide the “read” output state of a conventional eFuse circuit. The sensing circuit includes a comparator with one input coupled to the eFuse circuitry, and a second input coupled to a reference voltage generator circuit. The reference voltage generator circuit includes an internal resistor. Transistors of the sense circuit are provided to mimic the transistors of the eFuse circuit, so that variations of transistors due to process, voltage and temperature will be substantially the same. The resistor of the sense circuit is then effectively compared with the resistance of the eFuse by the comparator irrespective of temperature and process variations.

Abstract: An eFuse system that includes a mechanism that bridges banks of eFuses and allows the banks of eFuses to be placed any distance from each other. The bridging of the eFuse banks is transparent to compression and encode programming algorithm and hardware decode mechanisms. Thus, by using the mechanism for bridging gaps between eFuse banks, an eFuse subsystem with several banks distributed on an integrated circuit chip appears to be a single large eFuse bank to the encode/decode mechanisms of the integrated circuit. Additionally, with this mechanism, eFuse banks can be easily added or deleted.